High-speed cooking oven with optimized cooking efficiency

ABSTRACT

The present invention is directed to improving the conventional high-speed cooking oven based on a combination of hot air impingement and microwave heating by providing a time-dependent spatial variation in the net air impingement and/or net microwave energy applied to the food product in the oven. This is aimed at optimizing heat transfer and microwave efficiencies in a high-speed cooking oven, thereby enabling the oven to deliver an optimal cooking efficiency in comparison to the conventional high-speed cooking oven. In addition, under the present invention, the cooking efficiency may be further optimized by dimensioning the nozzles for hot air impingement to tighten impingement plumes, subject to the space constraint of the oven&#39;s cooking chamber, and dimensioning the cooking chamber of the oven in integer multiples of the wavelength of the microwave energy to match the microwave load. With the optimized cooking efficiency provided by the present invention, the high speed cooking technology may now be extended to ovens operating on a power supply based on a voltage less than 220 volts, preferably between 110 and 125 volts, with more productive results, so that the high-speed cooking technology may find a wider applicability and customer base.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation-in-part of co-pending U.S.patent application Ser. No. 11/803,787, filed on May 15, 2007, thecontents of which are incorporated herein by reference in theirentirety.

FIELD OF INVENTION

The present invention generally relates to an oven for cooking a foodproduct. More particularly, the present invention relates to ahigh-speed cooking oven with optimal cooking efficiency.

BACKGROUND OF THE INVENTION

Hot air impingement and microwave radiation are two different means forheating and cooking a food product based on different physicalprinciples. Hot air impingement is based on the transfer of heat from ahot air having a higher temperature to an object having a lowertemperature, changing the internal energy of the air and the object inaccordance with the first law of thermodynamics. On the other hand,microwave radiation consists of electromagnetic waves having a typicalwavelength of 12.24 cm or 4.82 inches and a frequency of 2,450 MHz,which are capable of causing dielectric heating of water, fat and sugarmolecules in a food product.

Initially, ovens based on hot air impingement and microwave ovens wereseparately developed and commercialized. However, it was laterdemonstrated that a combination of hot air impingement and microwaveradiation used in an oven can facilitate high-speed, high-qualitycooking. See, for example, U.S. Pat. No. 5,254,823 to McKee et al., U.S.Pat. No. 5,434,390 to McKee et al., U.S. Pat. No. 5,558,793 to McKee etal., and U.S. Pat. No. 6,060,701 to McKee et al. This led to thedevelopment and commercialization of quick-cooking hybrid ovens based onboth hot air impingement and microwave radiation and has established anew standard in the high-speed cooking technology.

While the technology of combining hot air impingement and microwaveheating to achieve high-speed cooking in an oven has by now been wellestablished, the current technology does not address a host of newchallenges created by such combination, including the problem ofinefficient energy use and consequent suboptimal cooking efficiency inthe existing high-speed cooking ovens. The fundamental principle ofcooking ovens is conversion of an available power (e.g., electric power)into heat energy to be directed to and absorbed by a food product in theoven to raise its internal temperature. Accordingly, the optimal cookingefficiency of an oven requires that the amount of heat energy convertedfrom a given power be maximized; the amount of the heat energy directedto a food product in the oven be maximized; and the amount of the heatenergy absorbed and retained by the food product be maximized. However,the current technology of the high-speed cooking ovens using both hotair impingement and microwave radiation is not directed to achievingsuch optimal cooking efficiency.

As a food product resides in a hot air environment of an oven,temperature gradients, or several boundary layers, form around thecooler food product. The oven cooks the food product by transferring theheat energy to the food product through these temperature gradients.Forced air convection by, for example, a fan can improve the heattransfer by “wiping away” the temperature gradients around the foodproduct and bringing the higher temperature air closer to the foodproduct. Hot air impingement can further improve the heat transfer by“piercing” the temperature gradients with jets of hot air and bringingthe air at higher temperature closer to the surface of the food product.However, significant portions of the electric power and the heat energyfrom the hot air impingement are lost in the process to the oven walls,various openings, plenum and air blower that form the hot aircirculation and delivery system of the oven. In addition, the presenceof a microwave launcher in the cooking chamber may further reduce theefficiency of heat transfer by the hot air impingement.

Another well-known problem with the technique of hot air impingement is“spotting” in the areas directly impacted by the hot air jets, causinguneven heating or scorching of the surface of the food product. Whilethis problem may be resolved by, for example, reduction in the hot airvelocity and/or increase in the diameter of the columns of impinging hotair, such solutions may further reduce the efficiency of the hot airimpingement.

In addition, the diameter/cross-sectional area of a column of hot airimpingement generally increases as the distance from the hot air jetorifice increases, thereby reducing the efficiency of hot airimpingement. While this problem may be solved by increasing the hot airvelocity, as discussed above, such solution may further aggravate thespotting problem.

As for the microwave portion of the conventional high-speed cookingoven, a portion of the electric power is lost to heat within thetransformer and magnetron during the process of generating microwaves.In addition, some portion of microwave energy is lost when reflectedfrom the cavity walls back to the magnetron and dissipated through thecooling fan. This can occur when there is an uneven matching between themicrowave delivery system and the microwave load.

Furthermore, it is also well known that microwave provides uneven heatenergy distribution across the volume of a cooking cavity. While thehorizontal unevenness may be eliminated by rotating the food productaround a vertical axis in the oven, as many conventional microwave ovensdo, such solution does little to reduce the vertical unevenness in theheat energy distribution.

There is yet another source of inefficiency in the conventionalhigh-speed cooking oven. Until the temperature at any portion of a foodproduct in the oven reaches 212° F. at which the water molecules in thefood product start being converted into steam during the cookingprocess, the amount of the energy absorbed by the food product roughlyequals the amount of the energy directed at the food product. However,after the point when the water starts to be converted into steam, aportion of the energy directed at the food product is not absorbed bythe food product, but is lost as the energy of activating the water intosteam, which subsequently escapes from the food product carrying away aportion of thermal energy from the food product. This phenomenon isfurther complicated by the fact that the heat energy absorbed at thesurface of the food product is not immediately dispersed downward belowthe surface due to the finite heat transfer coefficient (or thermalconductivity) of the food product and it takes some time to bring theinner mass of the food product into thermal equilibrium with thesurface. Accordingly, the efficiency in heat transfer to the foodproduct in the oven decreases after the temperature of the food surfacereaches 212° F., when the resulting steam at a higher temperature thanthe inner temperature of the food product carries away heat energy fromthe food product.

In summary, the problem with the current high-speed cooking technologybased on a combination of hot air impingement and microwave radiation isthat the combination has never been done in a way to optimize thecooking efficiency of the oven. With the suboptimal cooking efficiencyin the presence of various sources of inefficiencies in the conversionof electrical power to heat, the currently available high-speed cookingovens (either commercial models or residential models) operate on apower supply based on 220 volts or greater. As a result, this relativelyhigh electric power required to operate the high-speed cooking ovenlimits the universe of possible applications and customer bases,especially in residential households where a 120 volt-based power supplyis more common.

Thus, it is an object of the present invention to eliminate or reducesome of the inefficiencies in heat transfer present in the conventionalhigh-speed cooking ovens.

It is yet another object of the present invention to optimize thecooking efficiency of a high-speed cooking oven.

It is yet another object of the present invention to optimize thecombination of hot air impingement and microwave to seek the greatercooking efficiency than was possible in the conventional high-speedcooking oven.

It is yet another object of the present invention to optimize thecooking efficiency of the hot air impingement.

It is yet another object of the present invention to optimize thecooking efficiency of the microwave heating.

It is yet another object of the present invention to resolve thespotting problem without compromising the cooking efficiency of the hotair impingement.

It is yet another object of the present invention to provide a more evendistribution of microwave heating compared to the conventionalhigh-speed cooking oven.

It is yet another object of the present invention to match the cavity ofa high-speed cooking oven to the microwave load.

It is yet another object of the present invention to optimize theefficiency of heat transfer to a food product in the oven by overcomingthe inefficiency created by the heat loss due to the water steamescaping from the food product at 212° F. and the time lag in the heatenergy distribution in the inner mass of the food product due to itsfinite heat transfer coefficient.

It is yet another object of the present invention to provide ahigh-speed cooking oven that can operate on a power supply based onvoltage less than 220 volts.

It is yet another object of the present invention to provide ahigh-speed cooking oven that can operate on a power supply based on avoltage between 110 and 125 volts.

It is yet another object of the present invention to provide ahigh-speed cooking oven capable of operating on a power supply based onthe voltage of 120 volts and the current of 30 Amperes.

It is yet another object of the present invention to reduce theoperating costs of high-speed cooking ovens.

Other objects and advantages of the present invention will becomeapparent from the following description.

SUMMARY OF THE INVENTION

It has now been found that the above-mentioned and related objects ofthe present invention are obtained in the form of several separate, butrelated, aspects including an oven for cooking a food product at leastpartially by hot air impingement and/or at least partially by microwave.

More particularly, an oven for cooking a food product according to anexemplary embodiment of the present invention comprises a cookingchamber comprising a top and a support for receiving the food productfor cooking, a conduit for providing a gas into the cooking chamber, athermal energy source for heating the gas disposed in the conduit, afirst nozzle for causing a first impingement of the gas from the conduitinto the cooking chamber, a second nozzle for causing a secondimpingement of the gas from the conduit into the cooking chamber, and anair modulator for controlling respective flow rates of the gas for thefirst and the second impingements, wherein the first nozzle isconfigured and positioned to direct the first impingement of the gasgenerally toward a first side of the support, the second nozzle isconfigured and positioned to direct the second impingement of the gasgenerally toward a second side of the support, the first and the secondsides being generally opposite sides of the support, the first and thesecond nozzles are further configured and positioned to respectivelydirect the first and the second impingements of the gas to meet eachother at a distance from the support in the cooking chamber, and the airmodulator is adapted to cause a time-dependent spatial variation in thesum of the first and the second impingements of the gas applied to thefood product in the cooking chamber.

In at least one embodiment, the first side comprises a right edge of thesupport and the second side comprises a left edge of the support.

In at least one embodiment, the first and the second nozzles are furtherconfigured and positioned to respectively direct the first and thesecond impingements of the gas to meet each other above the midpointbetween the first and the second sides of the support in the cookingchamber.

In at least one embodiment, the first and the second nozzles are furtherconfigured and positioned to respectively direct the first and thesecond impingements of the gas to meet each other above the food producton the support in the cooking chamber.

In at least one embodiment, the first and the second nozzles aredimensioned to optimize the flow rates of the gas.

In at least one embodiment, the diameter of each of the first and thesecond nozzles is dimensioned to optimize the flow rate of thecorresponding nozzle.

In at least one embodiment, the length of each of the first and thesecond nozzles is dimensioned to optimize the flow rate of thecorresponding nozzle and the dimension of the cooking chambersimultaneously.

In at least one embodiment, the length of each of the first and thesecond nozzles is substantially 3 inches.

In at least one embodiment, the ratio of the inlet orifice area to theexit orifice area for each of the first and the second nozzles is set tooptimize the air impingement from the corresponding nozzle.

In at least one embodiment, the ratio of the inlet orifice area to theexit orifice area for each of the first and the second nozzles issubstantially 4 to 1.

In at least one embodiment, the respective directions of the first andthe second impingements of the gas are at a substantially 90-degreeangle with respect to each other.

In at least one embodiment, the first and the second nozzles are furtherconfigured to respectively direct the first and the second impingementsof the gas at a substantially 45-degree angle with respect to thesupport.

In at least one embodiment, the first nozzle is positioned at a firsthalf of the top and the second nozzle is positioned at a second half ofthe top.

In at least one embodiment, the air modulator is configured to provide afirst periodic modulation in time of the flow rate of the gas for thefirst impingement and a second periodic modulation in time of the flowrate of the gas for the second impingement, the first and the secondperiodic modulations having substantially the same amplitude and periodbut differing in phase by 180 degrees.

In at least one embodiment, the sum of the first and the second periodicmodulations is substantially constant in time.

In at least one embodiment, the first periodic modulation comprises afirst sinusoidal function in time for the flow rate of the firstimpingement and the second periodic modulation comprises a secondsinusoidal function in time for the flow rate of the second impingement,the first and the second sinusoidal functions having substantially thesame amplitude and period but differing in phase by 180 degrees.

In at least one embodiment, the oven further comprises a supportcontroller for modulating in time the distance of the support from thefirst and the second nozzles.

In at least one embodiment, the oven further comprises a third nozzlefor causing a third impingement of the gas from the conduit into thecooking chamber, the third nozzle being configured and positioned todirect the third impingement of the gas below the support.

In at least one embodiment, the conduit comprises a first return airexit and a second return air exit below the support in the cookingchamber, the first and the second return air exits being positioned onthe opposite sides of the cooking chamber respectively proximate to thefirst and the second sides of the support.

In at least one embodiment, the oven further comprises a return air exitcontroller for controlling the closing and the opening of each of thefirst and the second return air exits.

In at least one embodiment, the return air exit controller and the airmodulator are adapted to operate in synchronization.

In at least one embodiment, the return air exit controller is adapted toclose the first return air exit and open the second return air exit whenthe first air impingement is greater than the second air impingement,and to open the first return air exit and close the second return airexit when the second air impingement is greater than the first airimpingement.

In at least one embodiment, the oven is adapted to be powered by avoltage less than 220 volts.

In at least one embodiment, the voltage is between 110 and 125 volts.

In at least one embodiment, the oven further comprises one or moremagnetrons, a first microwave resonator for directing a first microwaveenergy generated by the one or more magnetrons into the cooking chamber,a second microwave resonator for directing a second microwave energygenerated by the one or more magnetrons into the cooking chamber, and amicrowave modulator for controlling each of the first and the secondmicrowave energies, wherein the first microwave resonator is configuredand positioned to direct the first microwave energy to propagategenerally toward the first side of the support, the second microwaveresonator is configured and positioned to direct the second microwaveenergy to propagate generally toward the second side of the support, thefirst and the second microwave resonators are further configured andpositioned to respectively direct the first and the second microwaveenergies to cross at a distance from the support in the cooking chamber,and the microwave modulator is adapted to cause a time-dependent spatialvariation in the sum of the first and the second microwave energiesapplied to the food product in the cooking chamber.

In at least one embodiment, the first side comprises a right edge of thesupport and the second side comprises a left edge of the support.

In at least one embodiment, the first and the second microwaveresonators are further configured and positioned to respectively directthe first and the second microwave energies to cross above the midpointbetween the first and the second sides of the support in the cookingchamber.

In at least one embodiment, the first and the second microwaveresonators are further configured and positioned to respectively directthe first and the second microwave energies to cross above the foodproduct on the support in the cooking chamber.

In at least one embodiment, the first and the second microwaveresonators are further configured and positioned to respectively directthe first and the second microwave energies to cross at the center ofthe food product on the support in the cooking chamber.

In at least one embodiment, the cooking chamber is dimensioned to matcha microwave load of the oven.

In at least one embodiment, the cooking chamber is dimensioned ininteger multiples of the wavelength of the first and the secondmicrowave energies.

In at least one embodiment, at least one of the length, width and heightof the cooking chamber is sized in integer multiples of the wavelengthof the first and the second microwave energies.

In at least one embodiment, the respective directions of the first andthe second microwave energies are at a substantially 90-degree anglewith respect to each other.

In at least one embodiment, the first and the second microwaveresonators are directed at a substantially 45-degree angle with respectto the support.

In at least one embodiment, the first microwave resonator is positionedat substantially near a first side of the top and the second microwaveresonator is positioned at substantially near a second side of the top,the first and the second sides being opposite sides of the top.

In at least one embodiment, the first side of the top comprises a leftedge of the top and the second side of the top comprises a right edge ofthe top.

In at least one embodiment, the microwave modulator comprises a voltageregulator for modulating a voltage for the one or more magnetrons.

In at least one embodiment, the microwave modulator comprises a switchfor turning on and off an electrical power to the one or moremagnetrons.

In at least one embodiment, the microwave modulator is configured toprovide a first periodic modulation in time of the first microwaveenergy and a second periodic modulation in time of the second microwaveenergy, the first and the second periodic modulations havingsubstantially the same amplitude and period but differing in phase by180 degrees.

In at least one embodiment, the sum of the first and the second periodicmicrowave modulations is substantially constant in time.

In at least one embodiment, the first periodic modulation comprises afirst sinusoidal function in time for the first microwave energy and thesecond periodic modulation comprises a second sinusoidal function intime for the second microwave energy, the first and the secondsinusoidal functions having substantially the same amplitude and periodbut differing in phase by 180 degrees.

In at least one embodiment, the oven further comprises a supportcontroller for modulating in time the distance of the support from thefirst and the second microwave resonators.

In at least one embodiment, the first and the second nozzles aredimensioned to prevent microwave resonances within the nozzles.

In at least one embodiment, the diameter of each of the first and thesecond nozzles is dimensioned to optimize the flow rate of thecorresponding nozzle and to prevent entry of the first or the secondmicrowave energies simultaneously.

In at least one embodiment, the diameter of each of the first and thesecond nozzles is substantially 0.75 inches.

In at least one embodiment, the microwave modulator is adapted tooperate in phase with the air modulator.

In at least one embodiment, the microwave modulator is adapted tooperate out of phase with the air modulator.

In at least one embodiment, each of the first and the second microwaveresonators comprises an upper resonator coupled to the one or moremagnetrons and a lower resonator with an opening to the cooking chamber.

In at least one embodiment, at least one width of the lower resonator issubstantially equal to the wavelength of a standing microwave in theupper resonator.

The present invention is also directed to an oven for cooking,comprising a cooking chamber comprising a top and a support forreceiving a food product for cooking, one or more magnetrons, a firstmicrowave resonator for directing a first microwave energy generated bythe one or more magnetrons into the cooking chamber, a second microwaveresonator for directing a second microwave energy generated by the oneor more magnetrons into the cooking chamber, and a microwave modulatorfor controlling the energy of each of the first and the second microwaveenergies, wherein the first microwave resonator is configured andpositioned to direct the first microwave energy to propagate generallytoward a first side of the support, the second microwave resonator isconfigured and positioned to direct the second microwave energy topropagate generally toward a second side of the support, the first andthe second sides being generally opposite sides of the support, thefirst and the second microwave resonators are further configured andpositioned to respectively direct the first and the second microwaveenergies to cross at a distance from the support in the cooking chamber,and the microwave modulator is adapted to cause a time-dependent spatialvariation in the sum of the first and the second microwave energiesapplied to the food product in the cooking chamber.

In at least one embodiment, the first side comprises a right edge of thesupport and the second side comprises a left edge of the support.

In at least one embodiment, the first and the second microwaveresonators are further configured and positioned to respectively directthe first and the second microwave energies to cross above the midpointbetween the first and the second sides of the support in the cookingchamber.

In at least one embodiment, the first and the second microwaveresonators are further configured and positioned to respectively directthe first and the second microwave energies to cross above the foodproduct on the support in the cooking chamber.

In at least one embodiment, the first and the second microwaveresonators are further configured and positioned to respectively directthe first and the second microwave energies to cross substantially atthe center of the food product on the support in the cooking chamber.

In at least one embodiment, the cooking chamber is dimensioned to matcha microwave load of the oven.

In at least one embodiment, the cooking chamber is dimensioned ininteger multiples of the wavelength of the first and the secondmicrowave energies.

In at least one embodiment, at least one of the length, width and heightof the cooking chamber is sized in integer multiples of the wavelengthof the first and the second microwave energies.

In at least one embodiment, the respective directions of the first andthe second microwave energies are at a substantially 90-degree anglewith respect to each other.

In at least one embodiment, the first and the second microwaveresonators are directed at a substantially 45-degree angle with respectto the support.

In at least one embodiment, the first microwave resonator is positionedat substantially near a first side of the top and the second microwaveresonator is positioned at substantially near a second side of the top,the first and the second sides being opposite sides of the top.

In at least one embodiment, the first side of the top comprises a leftedge of the top and the second side of the top comprises a right edge ofthe top.

In at least one embodiment, the microwave modulator comprises a voltageregulator for modulating a voltage for the one or more magnetrons.

In at least one embodiment, the microwave modulator comprises a switchfor turning on and off an electrical power to the one or moremagnetrons.

In at least one embodiment, the microwave modulator is configured toprovide a first periodic modulation in time of the first microwaveenergy and a second periodic modulation in time of the second microwaveenergy, the first and the second periodic modulations havingsubstantially the same amplitude and period but differing in phase by180 degrees.

In at least one embodiment, the sum of the first and the second periodicmodulations is substantially constant in time.

In at least one embodiment, the first periodic modulation comprises afirst sinusoidal function in time for the first microwave energy and thesecond periodic modulation comprises a second sinusoidal function intime for the second microwave energy, the first and the secondsinusoidal functions having substantially the same amplitude and periodbut differing in phase by 180 degrees.

In at least one embodiment, the oven further comprises a supportcontroller for modulating in time the distance of the support from thefirst and the second microwave resonators.

In at least one embodiment, the oven is adapted to be powered by avoltage less than 220 volts.

In at least one embodiment, the voltage is between 110 and 125 volts.

In at least one embodiment, each of the first and the second microwaveresonators comprises an upper resonator coupled to the one or moremagnetrons and a lower resonator with an opening directed to the cookingchamber.

In at least one embodiment, at least one width of the lower resonator issubstantially equal to the wavelength of a standing microwave in theupper resonator.

The present invention is also directed to an oven for cooking a foodproduct, comprising a cooking chamber comprising a top, a bottom, and asupport for receiving the food product for cooking, one or moremagnetrons, one or more microwave resonators for directing a microwaveenergy generated by the one or more magnetrons into the cooking chamber,a conduit and one or more air blowers for providing a gas into thecooking chamber, a thermal energy source for heating the gas disposed inthe conduit, a first tube for generating a first plume array of theheated gas from the conduit and introducing it into the cooking chamber,and a second tube for generating a second plume array of the heated gasfrom the conduit and introducing it into the cooking chamber, whereinthe first and the second tubes are configured to respectively direct thefirst and the second plume arrays towards substantially oppositeportions of the support at a non-zero angle less than 90 degrees withrespect to the surface of the support, with the directions of the firstand the second plume arrays crossing each other above the food producton the support in the cooking chamber.

In at least one embodiment, the oven further comprises an elevator foradjusting the height of the support.

In at least one embodiment, the height of the support is dynamicallyadjustable to optimize the cooking efficiency and power consumption forcooking the food product.

In at least one embodiment, the oven further comprises a return airopening for allowing the gas from the first and the second plume arraysto return from the cooking chamber to the conduit.

In at least one embodiment, the return air opening comprises a firstreturn air opening positioned substantially at or along the intersectionof the direction of the first plume array and the cooking chamber wall,and a second return air opening positioned substantially at or along theintersection of the direction of the second plume array and the cookingchamber wall.

In at least one embodiment, the conduit comprises one or more bottom airinlets, positioned substantially at the bottom of the cooking chamber,for diverting a portion of the heated gas to the bottom of the cookingchamber and directing it to the underside of the support.

In at least one embodiment, the oven further comprises an air modulatorfor controlling a flow rate of the heated gas through the one or morebottom air inlets.

In at least one embodiment, the air modulator comprises a damper valvefor the one or more bottom air inlets.

In at least one embodiment, the air modulator comprises a bottom airdiverter.

In at least one embodiment, the air modulator comprises a deflector inthe conduit for hot air or in an air inlet housing encasing the inletsto the tubes.

In at least one embodiment, the one or more microwave resonatorscomprise one or more waveguides.

In at least one embodiment, each of the one or more microwave resonatorscomprises an upper resonator coupled to the one or more magnetrons and alower resonator with an opening to the cooking chamber.

In at least one embodiment, the lower resonator comprises two feedhoms,each having a top aperture to the upper resonator and a bottom apertureto the cooking chamber.

In at least one embodiment, the two feedhoms are placed substantially inparallel, but diagonally off-set with respect to each other.

In at least one embodiment, each of the two feedhoms is in the shape ofa truncated rectangular pyramid with the bottom rectangular aperturecorresponding to the base of the pyramid, and the top rectangularaperture is smaller than the bottom rectangular aperture.

In at least one embodiment, the dimensions of the microwave resonatorare designed to optimize the microwave-to-heat energy conversion.

In at least one embodiment, each of the first and the second tubescomprises a tube inlet coupled to the conduit and a tube outlet to thecooking chamber.

In at least one embodiment, each of the first and the second tubes is inthe shape of an inverted truncated triangular prism with the tube inletcorresponding to the base of the prism.

In at least one embodiment, the area of the tube inlet is larger thanthe area of the tube outlet at a ratio substantially sufficient forforming a tight plume of the heated gas.

In at least one embodiment, the dimensions of the first and the secondtubes are designed to optimize the formation of a plume of the heatedgas having a long and narrow rectangular cross section.

In at least one embodiment, the oven further comprises a first flap anda second flap for respectively covering the first and the second tubes.

In at least one embodiment, the oven further comprises one or moremotors for driving the first and the second flaps to open and close.

In at least one embodiment, the one or more motors are configured toopen only one of the first and the second flaps, while keeping the otherclosed.

In at least one embodiment, the oven further comprises one or more leverarms driven by one or more solenoids to open and close the first and thesecond flaps.

In at least one embodiment, the oven further comprises a first flap anda second flap for respectively covering the tube inlets of the first andthe second tubes.

In at least one embodiment, each of the first and the second flaps hassubstantially louvered edges to minimize air leakage when closed.

In at least one embodiment, each of the first and the second tubescomprises one or more spacers to keep the microwave energy from enteringthe tube.

In at least one embodiment, the one or more air blowers comprise a firstair blower for directing the heated gas in the conduit to the first andthe second tubes, and a second air blower for directing the heated gasin the conduit to the one or more bottom air inlets, wherein the firstand the second air blowers are independently controllable.

In at least one embodiment, the one or more air blowers comprise asingle speed air blower.

In at least one embodiment, the one or more microwave resonatorscomprise a first microwave resonator for directing a first microwaveenergy generated by the one or more magnetrons into the cooking chamber,and a second microwave resonator for directing a second microwave energygenerated by the one or more magnetrons into the cooking chamber,wherein the first and the second microwave resonators are configured torespectively direct the first and the second microwave energies topropagate generally towards substantially opposite portions of thesupport at a non-zero angle less than 90 degrees with respect to thesurface of the support, with the propagation directions of the first andthe second microwave energies crossing each other at a distance from thesupport in the cooking chamber.

In at least one embodiment, the one or more magnetrons comprise a firstmagnetron for generating the first microwave energy, and a secondmagnetron for generating the second microwave energy.

In at least one embodiment, the propagation directions of the first andthe second microwave energies are at a substantially 45-degree anglewith respect to the surface of the support.

In at least one embodiment, the cooking chamber is dimensioned to matcha microwave load of the oven.

In at least one embodiment, the cooking chamber is dimensioned ininteger multiples of the wavelength of the microwave energy.

In at least one embodiment, at least one of the length, width and heightof the cooking chamber is sized in integer multiples of the wavelengthof the microwave energy.

In at least one embodiment, the first microwave resonator is positionedsubstantially near a first side of the top of the cooking chamber andthe second microwave resonator is positioned substantially near a secondside of the top of the cooking chamber, the first and the second sidesbeing opposite sides of the top.

In at least one embodiment, the first side of the top comprises a leftedge of the top and the second side of the top comprises a right edge ofthe top.

In at least one embodiment, the oven further comprises a microwavemodulator for controlling each of the first and the second microwaveenergies.

In at least one embodiment, the microwave modulator is adapted to causea time-dependent spatial variation in the sum of the first and thesecond microwave energies applied to the food product in the cookingchamber.

In at least one embodiment, the microwave modulator comprises a voltageregulator for modulating a voltage for the one or more magnetrons.

In at least one embodiment, the microwave modulator comprises a switchfor turning on and off an electrical power to the one or moremagnetrons.

In at least one embodiment, the oven further comprises an air modulatorfor controlling respective flow rates of the heated gas through thefirst and the second tubes.

In at least one embodiment, the air modulator is adapted to cause atime-dependent spatial variation in the sum of the first and the secondplume arrays applied to the food product in the cooking chamber.

In at least one embodiment, the directions of the first and the secondplume arrays are at a substantially 45-degree angle with respect to thesurface of the support.

In at least one embodiment, the first tube is positioned substantiallythrough a first half of the top of the cooking chamber, and the secondtube is positioned substantially through a second half of the top.

In at least one embodiment, the conduit comprises a common top air inletplenum enclosing the tube inlets for both of the first and the secondtubes.

In at least one embodiment, the conduit comprises two separate top airinlet plenums respectively enclosing the tube inlets for the first tubeand the tube inlets for the second tube.

In at least one embodiment, the first tube is adapted to focus the firstplume array substantially at one side of the support, when the secondtube is closed, the second tube is adapted to focus the second plumearray substantially at the opposite side of the support, when the firsttube is closed, and the first and the second tubes are adapted to focusthe sum of the first and the second plume arrays substantially at thecenter of the support, when both are open.

In at least one embodiment, the oven further comprises a first returnair opening positioned substantially at or along the intersection of thedirection of the first plume array and the cooking chamber wall, and asecond return air opening positioned substantially at or along theintersection of the direction of the second plume array and the cookingchamber wall.

In at least one embodiment, the first and the second tubes areconfigured to optimize the utilization of the first and the second plumearrays for cooking the food product whose surface area is substantiallysmaller than the surface area of the support.

In at least one embodiment, the oven is adapted to be powered by avoltage less than 220 volts.

These and other features of this invention are described in, or areapparent from, the following detailed description of various exemplaryembodiments of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and related objects, features and advantages of the presentinvention will be more fully understood by reference to the following,detailed description of the preferred, albeit illustrative, embodimentof the present invention when taken in conjunction with the accompanyingfigures, wherein:

FIG. 1 illustrates a sectional view of an exemplary embodiment of thepresent invention.

FIG. 2 illustrates another sectional view thereof taken along the line2-2 of FIG. 1.

FIG. 3 illustrates yet another sectional view thereof taken along theline 3-3 of FIG. 1.

FIGS. 4A, 4B and 4C respectively illustrate various positions of an airmodulating cover for controlling the flow rate of the nozzles for airimpingement.

FIGS. 5A, 5B and 5C respectively illustrate various positions of an airmodulating cover in an alternative embodiment viewed from the top.

FIGS. 6A, 6B, 6C, and 6D illustrate a tube used for hot air impingementin yet another alternative embodiment of the present invention.

FIGS. 7A, 7B and 7C illustrate various views of a microwave resonator inanother alternative embodiment of the present invention.

FIGS. 8A, 8B, and 8C illustrate various views of another embodiment ofthe present invention.

FIGS. 9A, 9B, and 9C illustrate various views of another embodiment ofthe present invention.

FIGS. 10A, 10B, and 10C illustrate various views of another embodimentof the present invention.

FIGS. 11A, 11B, and 11C respectively illustrate plume arrays generatedby two tubes in at least one embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the present invention will be described in terms of a stand-aloneor counter-top high-speed cooking oven, it will be apparent to thoseskilled in the art that an oven according to the present invention mayalternatively be implemented as a wall unit, a console model having feetadapted to rest on the floor, part of a vending machine, or othervariations thereof.

Referring now to the drawings, in particular to FIGS. 1-3 thereof,therein illustrated is a hybrid oven based on a combination of hot airimpingement and microwave according to an exemplary embodiment of thepresent invention, generally designated by the reference numeral 100. Itis first noted that these figures are merely schematic illustrations ofan exemplary embodiment of the present invention based on varioussectional views and are not intended to reflect the exact dimensions,scales or relative proportions of the oven 100 or components thereof, orthe full engineering specification thereof, which should be apparent tothose skilled in the art. FIG. 1 is a frontal sectional view of theoven, while FIG. 2 is a side sectional view of the oven taken along theline 2-2 of FIG. 1 and FIG. 3 is another side sectional view of the oventaken along the line 3-3 of FIG. 1. The oven 100 comprises a cookingchamber generally designated 101, which is adapted to receive a foodproduct 114 to be placed on a support 112 for cooking. FIGS. 2 and 3illustrate a door 201 through which the food product 114 can be receivedby the cooking chamber 101.

The support 112 may comprise a horizontally planar top surface tosupport the food product 114 and its corresponding bottom surface. Thesupport may further comprise one or more holes or openings therein tofacilitate gaseous communication between above the top surface and belowthe bottom surface of the support 112. The support 112 may be of anyfeasible shape, common shapes including rectangular and circular shapes.Referring to FIG. 1, when the “right side” and the “left side” of thesupport 112 are referred to in the following description, they areintended to refer to the two opposite sides of the support 112 as viewedin FIG. 1, wherein the “right” and the “left” are defined by the rightand the left side walls of the cooking chamber 101. In alternativeembodiments, the support 112 for receiving and holding a food product inthe cooking chamber 101 may be in a non-planar form, such ashorizontally or vertically positioned skewer. In these cases, the“right” and the “left” sides of the support correspond to the oppositeends of the skewer. It should be appreciated that the “left” and the“right” sides of the support as referred to in the description depend onthe physical configuration of the support and the cooking chamber.

In at least one alternative embodiment of the present invention, thesupport 112 may be in the form of an elevator or may be coupled to anelevating mechanism so that the height of the support 112 with respectto the top and bottom of the cooking chamber may be dynamically adjustedduring the cooking. As discussed further below, the dynamical adjustmentof the height of the support 112 during the operation of the cookingoven may be used to optimize the cooking efficiency and powerconsumption of the cooking oven.

The cooking chamber 101, return air plenums 119, 120, an air conduit 202and an air inlet housing 111 form an air circulation and delivery systemof the oven 100. The terms “air” and “airflow” are used interchangeablywith “gas” and “gas flow” in this description unless otherwise noted. Asshown in FIG. 1, the return air plenums 119, 120 may be positionedadjacent to the bottom portion of the cooking chamber 101 and areadapted for gaseous communication with the cooking chamber 101 throughreturn air exit holes 115, 116. FIG. 1 shows that these return air exitholes 115, 116 are positioned below and in the proximity of the left andthe right sides of the support 112, respectively. They are adapted toreceive the air flow from within the cooking chamber 101 to be guided tothe air conduit 202. While not shown in the figure, the return air exitholes 115, 116 may comprise gates which can be opened or closed based onan external control.

The return air plenums 119, 120 are connected to an air conduit 202(shown in FIG. 2), which may be vertically disposed on the back side ofthe oven 100 opposite from the oven door 201. The air conduit 202 allowsgaseous communication between the return air plenums 119, 120 and theair inlet housing 111 positioned on the top of the cooking chamber 101.For the sake of simplicity, the interconnected air circulation anddelivery system of the air conduit 202, the return air plenums 119, 120,and the air inlet housing 111 will be referred to as a conduit. Whilenot shown in the figures, a thermal energy source, such as parallelheating coils, may be coupled to or disposed in the air conduit 202 toheat the air disposed therein. In an alternative embodiment, instead ofa single joint air conduit 202, each of the return air plenums 119, 120may have its own air conduit for gaseous communication with the airinlet housing 111. FIGS. 2 and 3 show a hot air blower 203 whichcirculates the air in the air circulation and delivery system defined bythe cooking chamber 101, the return air plenums 119, 120, the return airconduit 202 and the air inlet housing 111, and provides the desired hotairflow onto the food product 114 placed on the support 112 in thecooking chamber 101.

The air inlet housing 111 positioned on the top of the cooking chamber101 provides the hot air flow in the form of air impingement into thecooking chamber 101 through at least two nozzles (or impingement tubes)108 and 109. The two sets of nozzles 108 and 109 are respectivelypositioned on the opposite sides of a semi-cylindrical base 126 (shownas a semi-circle in the sectional view in FIG. 1) on the top of thecooking chamber 101 in the air inlet housing 111. FIG. 3 shows a row ofsix nozzles 109 on one side of the base 126. While not shown in anyfigure, there is another row of six nozzles 108 on the other side of thebase 126, with each of the nozzles 108 positioned on one side of thebase 126 directly opposite to the corresponding one of the nozzles 109on the other side of the base 126. Each nozzle 108, 109 has a tubularstructure of a given height, and is subtended at one end by a circularinlet orifice 117 positioned within the air inlet housing 111 and at theopposite end by a circular exit orifice 118 protruding in the cookingchamber 101. The nozzle exit orifices direct columnated flows of hot air(air impingement) into the cooking chamber 101. The nozzles arepreferably made of a suitably strong and sturdy material (e.g., steel)that can withstand the temperature and pressure of the hot air flowingor being blown through the nozzles.

In at least one alternative embodiment of the present invention, inaddition to the nozzles 108 and 109 shown in FIG. 1, or other means ofhot air impingement protruding substantially from the top of the cookingchamber 101, one or more air inlets or another set of nozzles may beplaced below the support 112 substantially at the bottom of the cookingchamber 101 to direct a hot air flow or hot air impingement to theunderside of the support 112. In this exemplary embodiment, the conduitmay further comprise a bottom air plenum from which the heated air maybe directed to the underside of the support 112 via the one or more airinlets or bottom nozzles. The bottom air plenum is connected to the airconduit 202 and/or the air inlet housing 111 to divert a portion of theheated air to the bottom of the cooking chamber.

The amount of the heated air diverted from the air conduit 202/air inlethousing 111 to the bottom air plenum may be controlled or modulated byusing a damper valve or a bottom air diverter. Alternatively, or inaddition, the air inlet housing 111 may further comprise a deflector,which can affect the amount of heated air diverted to the bottom airplenum relative to the amount of the hot air flow from the top of thecooking chamber. By controlling the diversion of the heated air into thebottom air plenum, one can also control the amount of the heated airintroduced from the top of the cooking chamber 101 through, for example,the top nozzles 108 and 109, thereby modulating its flow rate andvelocity. In this way, even if the hot air blower 203 is driven by asingle speed motor, one can achieve the substantially similar kind ofhot air flow modulations that can be achieved by a significantly moreexpensive variable speed blower.

In at least one alternative embodiment of the present invention, insteadof just one hot air blower 203 for the entire conduit, there may be twoindependently controllable hot air blowers, one for directing the heatedgas in the conduit to the air inlet housing 111 on the top of thecooking chamber 101, and the other for directing the heated gas to thebottom air plenum.

It is also noted that by dynamically adjusting the height of the support112 and thereby changing the distance of the food product 114 to the topnozzles 108 and 109 relative to the bottom air inlets or nozzles, onemay achieve the effect substantially similar to the one achieved bymodulating the amount of hot air flowing through the top nozzles 108 and109 relative to the one flowing through the bottom air inlets ornozzles, with the support 112 being kept at a constant height.

In yet another alternative embodiment of the present invention (e.g.,wherein the support for the food product in the cooking chamber is ahorizontally positioned skewer), in addition to or as an alternative tothe nozzles 108 and 109 protruding from the top of the cooking chamber101, two corresponding sets of nozzles may be positioned to protrudefrom the bottom of the cooking chamber 101 to project the airimpingements upwards towards the food product supported by thehorizontal skewer. In yet another alternative embodiment of the presentinvention (e.g., wherein the support for the food product in the cookingchamber is a vertically positioned skewer), instead of the nozzles 108and 109 protruding from the top of the cooking chamber, two sets ofnozzles may be positioned to protrude respectively from, for example,the upper portion and the lower portion of a side wall of the cookingchamber. It should be appreciated that, depending on the physicalconfiguration of the cooking chamber and the support for a food producttherein, two sets of nozzles for the air impingement may be positionedin various possible places in the cooking chamber to accomplish thesubstantially similar “sweeping” effects that are to be described below.

Referring back to FIG. 1, two sets of nozzles (i.e., the left nozzles108 and the right nozzles 109) on the opposite sides of the base 126 areadapted to direct the air impingements in respective directions 123 and124 as indicated by the dotted lines coming out of the correspondingexit orifices. These directions 123 and 124 are at an angle with respectto the vertical axis of the cooking chamber 101 (or the horizontal planeof the support 112) and cross at a point 127 above the support 112,preferably vertically above the midpoint between the left and the rightsides of the support 112 and preferably above the upper surface of anyfood product 114 placed on the support 112. In this configuration, therespective air impingements coming out of the left and the right nozzles108 and 109 at the same time at the given angle would collide at thecrossing point 127 at a distance from the support 112. If the energiesof the air impingements from both nozzles 108 and 109 are equal (i.e.,if the flow rates of both nozzles 108 and 109 are same), the net resultof such collision would be a net air impingement directed substantiallyvertically downward from the crossing point 127 toward the point on thesupport directly below the crossing point 127, preferably the midpointbetween the left and the right sides of the support 112. In analternative embodiment wherein two sets of nozzles are positioned toprotrude from the bottom of the cooking chamber and configured toproject the air impingements upwards, the crossing point of therespective air impingements may be located below the support for thefood product in the cooking chamber. In yet another alternativeembodiment wherein the support is vertically positioned (e.g., avertical skewer) and two sets of nozzles are positioned to protrude froma side wall of the cooking chamber, the crossing point of the respectiveair impingements may be located at a horizontal distance from thevertical midpoint of the support.

As indicated by the direction 123, the nozzle 108 on the left side ofthe base 126 directs the air impingement toward the right half of thecooking chamber 101, preferably toward a general area in the proximityof the right side of the support 112. In mirror symmetry, the nozzle 109on the right side of the base 126 directs the air impingement toward theleft half of the cooking chamber 101, as indicated by the direction 124,preferably toward a general area in the proximity of the left side ofthe support 112. Accordingly, the left and the right nozzles 108 and 109are configured to generally direct the respective air impingements tothe opposite portions of the food product 114 placed on the support 112.It should be appreciated that the “left side” and the “right side” ofthe support 112 to which the respective air impingements from thenozzles 109 and 108 are generally directed may correspond to anyopposite portions of a food product placed on or held by the support.There may be various possible choices for the “left side” and the “rightside” of the support depending on the physical configuration of thesupport and the cooking chamber.

The angle formed by the directions 123 and 124 with respect to thevertical axis of the cooking chamber 101 is determined by where therespective air impingements from the nozzles 108 and 109 are targeting.As an example, FIG. 1 shows that the directions 123 and 124 form anangle of roughly 45 degrees with respect to the vertical axis of thecooking chamber 101 and meet at the crossing point 127 at an angle ofroughly 90 degrees. However, these angles may vary depending on thedimensions of the cooking chamber 101 and the support 112, as well asthe relative positions of the nozzles 108 and 109.

A flow rate of a nozzle may be determined by the dimension of the nozzleand the pressure of hot air into the nozzle. By controlling the inputarea of the nozzle for the hot air to flow through and therebyeffectively changing the dimension of the nozzle, one may modulate theflow rate of the nozzle and consequently its corresponding airimpingement applied to the food product 114 in the cooking chamber 101.This air modulation can be achieved by various means, including bothmanual and automatic control means. As an example, FIG. 1 shows that theoven 100 has an air modulator in the form of a cover 125 impermeable tothe air that is configured for and capable of rotationally sliding overthe outer surface of the semi-cylindrical base 126 containing two rowsof the nozzle inlet orifices 117. This air modulating cover 125 isdimensioned to completely cover, at one time, a portion of the surfaceof the semi-cylindrical base 126 containing one row of the nozzle inletorifices 117 so that no hot air may flow into the corresponding nozzles,while allowing the hot air in the air inlet housing 111 to flow into thenozzles positioned on the opposite side of the base 126. This situationis illustrated in FIGS. 4A and 4C. In FIG. 4A, the air modulating cover125 is positioned to cover the row of the nozzle inlet orifices on theleft side of the base 126 so that the air impingement is generated onlythrough the nozzles 109 on the right side of the base 126. In FIG. 4C,the air modulating cover 125 is now positioned to cover the row of thenozzle inlet orifices on the right side of the base 126 so that the airimpingement is generated only through the nozzles 108 on the left sideof the base 126. When positioned properly, the air modulating cover 125may be dimensioned to allow the equal amount of hot air in the air inlethousing 111 to flow into each nozzle in the both rows of nozzles 108 and109 on the opposite sides of the base 126. This is illustrated in FIG.4B.

As shown in FIG. 1, the position of the air modulating cover 125 on theouter surface of the base 126 may be controlled manually by a handle110, which is coupled to the air modulating cover 125 through a hingepoint 128. In this configuration, a manual torque may be exerted on thehandle 110 to rotate the position of the air modulating cover 125 aroundthe hinge point 128.

In an alternative embodiment, the position of the air modulating cover125 may be controlled automatically by, for example, a suitableelectromechanical control device known to those skilled in the art. Suchautomatic control means may facilitate a periodic change in the positionof the cover 125 to create periodic modulations (e.g., sinusoidalmodulations, periodic step function modulations, etc.) in time of therespective flow rates for the nozzles 108 on the left side of the base126 and the nozzles 109 on the right side of the base 126. This periodicchange in the position of the air modulating cover 125 to cover thenozzles 108 on the left side of the base 126 and the nozzles 109 on theright side of the base 126 alternatively in time may provide respectiveperiodic modulations in the flow rate of the left and the right set ofnozzles 108 and 109 that have the same amplitude and period, but differin phase by 180 degrees. When the total amount of the hot air disposedin the air inlet housing 111 is maintained to be constant, the sum ofthe periodically modulated flow rates for the both sets of nozzles 108and 109 also remains constant in time.

In another alternative embodiment, the side edges of the air modulatingcover 125, which respectively slide over the inlet orifices of the leftand the right nozzles 108 and 109 during the modulation of therespective flow rates, may be specially shaped or indented to facilitatea more gradual modulation in the flow rates in time and a gradualtransition between the opening and the closing of the nozzles. FIGS.5A-5C illustrate various positions of one exemplary air modulating cover125, viewed from the top, comprising side edges having triangularindents at the positions corresponding to the nozzle inlet orifices onthe surface of the base 126. FIG. 5A shows the left side edge of the airmodulating cover 125 just starting to partially cover the inlet orificesof the left nozzles 108. If the side edges were straight as illustratedin FIG. 3, the air modulating cover 125 would have covered the half ofthe input area of the inlet orifices of the left nozzles 108, butbecause of the triangular indents on the side edge, the air modulatingcover 125 only a small portion of the inlet orifices. FIG. 5B shows theleft side edge of the air modulating cover 125 partially covering theinlet orifices of the left nozzles 108. Again, if the side edge werestraight, the air modulating cover 125 would have completely covered theinlet orifices, but because of the triangular indents, there are smallopenings between the air modulating cover 125 and the inlet orifices tolet the hot air to flow through. FIG. 5C illustrates the position of theair modulating cover 125 in which the inlet orifices of the left nozzles108 are finally and completely covered by the cover. Instead oftriangular indents, one may alternatively use elliptical indents,semicircular indents or any other shape of the side edges of the airmodulating cover 125 that may facilitate a gradual transition betweenthe opening and the closing of the inlet orifices of the nozzles 108 and109 by the air modulating cover 125.

In yet another alternative embodiment of the present invention, insteadof the air modulating cover 125, an air modulator may comprise otherfeasible means of controlling the flow rate of the hot air through eachnozzle. For example, each nozzle may have a gate-like structure whichmay be shut or open based on an external switch or a command from anexternal control unit. Such gate-like structure may be placed either atthe nozzle inlet orifice, or at the nozzle exit orifice, or at any othersuitable place within the nozzle. In another example, the gate-likestructure may be capable of varying or adjusting, possibly periodically,the size of the opening through an external control to permit a desiredmodulation of the flow rate through the nozzle.

The configuration of the nozzles 108, 109 and the air modulating cover125 for controlling the flow rate of each nozzle as illustrated in FIG.1 and described above may be operated to cause a time-dependent spatialvariation in the net impact or net energy profile of the air impingementapplied to the food product 114 placed on the support 112 in the cookingchamber 101 in the following exemplary way. Referring to both FIGS. 1and 4A, for a predetermined time period, the air modulating cover 125 ispositioned on the left side of the base 126 completely covering theinlet orifices of the left nozzles 108, thereby allowing only the rightnozzles 109 to provide the air impingement into the cooking chamber 101.As indicated by the general direction 124 of the air impingement fromthe right nozzles 109, this configuration causes the net impact orenergy of the air impingement from the nozzles to be concentrated in thearea in the left half of the cooking chamber 101 where the right nozzles109 are targeting, preferably in the general area in the proximity ofthe left side of the support 112.

After this time period, as the air modulating cover 125 rotationallyslides to the right, away from the inlet orifices of the left nozzles108, the amount of hot air introduced into the left nozzles 108increases from zero and at the same time, the amount of the hot airavailable to the right nozzles 109 starts to decrease. The resultingincreasing momentum of the air impingement from the left nozzles 108 inthe general direction 123, which collides with the air impingement fromthe right nozzles 109 at the crossing point 127, would cause the areawhere the net impact or energy of the air impingement is concentrated tomove to the right on the support 112.

Now referring to FIGS. 1 and 4B, for another predetermined time period,the air modulating cover 125 is positioned between the inlet orifices ofthe left and the right nozzles 108 and 109 so that it allows the equalamounts of the hot air to flow into both the left and the right nozzles108 and 109. As described above, the respective air impingements havingthe same energies coming out of the left and the right nozzles 108 and109 at the same time collide at the crossing point 127, and as a result,the net air impingement is directed vertically downward from thecrossing point 127 to the support 112, preferably to the midpointbetween the left and the right sides of the support 112. Accordingly,the area where the net impact or energy of the air impingement isconcentrated has moved from the left and is now in the general area inthe middle of the support 112 or the upper surface of the food product114 above this general area.

After this time period, as the air modulating cover 125 rotationallyslides further to the right, to cover the inlet orifices of the rightnozzles 109, the amount of hot air introduced into the right nozzles 109steadily decreases to zero. The resulting decrease in the momentum ofthe air impingement from the right nozzles 109 in the general direction124 would cause the net impact area of the air impingement to furthermove toward the right on the support 112.

Referring now to both FIGS. 1 and 4C, for yet another predetermined timeperiod, the air modulating cover 125 is now positioned on the right sideof the base 126 completely covering the inlet orifices of the rightnozzles 109, thereby allowing only the left nozzles 108 to provide theair impingement into the cooking chamber 101. As indicated by thegeneral direction 123 of the air impingement from the left nozzles 108,this configuration causes the net impact or energy of the airimpingements from the nozzles to be concentrated in the area in theright half of the cooking chamber 101 where the left nozzles 108 aretargeting, preferably in the general area in the proximity of the rightside of the support 112.

In this way, the concentration of the net impact/energy of the airimpingement from the nozzles may “sweep” across the food product 114 inthe cooking chamber 101 from the left to the right and vice versa overtime in a controlled manner, thereby facilitating even horizontaldistribution of heat energy transfer from the air impingement to thefood product and further improving the cooking efficiency of the oven100. Furthermore, compared to the conventional high-speed cooking ovensbased on air impingement, this capability of providing a time-dependentspatial variation of the net impact/energy profile of the airimpingement helps to reduce the heat energy loss to the walls of thecooking chamber 101, and minimize the needs for a variable speed motorfor the hot air blower 203, the air velocity modulation throughdampening, or the modulation of the air heat through adjusting the powerof the thermal energy source in the conduit 202. All of these add up tooptimize the overall cooking efficiency of the oven 100.

The capability of providing a time-dependent spatial variation of thenet impact/energy profile of the air impingement may also be applied toovercome or alleviate the inefficiency arising from the water steamcarrying away thermal energy from the food product starting at thetemperature of 212° F. as described in the Background section. Forexample, referring to FIGS. 1 and 4A-C, the air modulating cover 125 isfirst positioned as illustrated in FIG. 4A so that the net energy of theair impingement is concentrated in the proximity of the surface of theleft side of the food product 114. This configuration is maintaineduntil the left side of the food product 114 reaches a temperatureslightly under 212° F. Next, the air modulating cover 125 is positionedas illustrated in FIG. 4B, causing the net energy of the air impingementto be generally concentrated in the middle of the food product 114. Whenthe surface of the middle portion of the food product 114 reaches atemperature slightly under 212° F., then the air modulating cover 125rotationally slides further to the right as illustrated in FIG. 4C,causing the net energy of the air impingement to be concentrated in theproximity of the surface of the right side of the food product 114. Thisconfiguration is maintained until the temperature of the surface of theright side of the food product 114 reaches slightly under 212° F.Meanwhile, the heat energies previously transferred to the surfaces ofthe left side and the middle portion of the food product 114 aredispersed downward below the surface to heat up the inner mass of thefood product 114. The above air modulating steps may be repeated,periodically in time, until the internal temperature of the food product114 in the cooking chamber 101 reaches a desired level.

By maintaining the temperature of the different portions of the surfaceof the food product 113 slightly under 212° F. and allowing them todisperse the transferred heat energies to the inner mass of the foodproduct alternately at different times, the loss of thermal energy tothe water steam from the surface of the food product may be minimizedand therefore the efficiency of heat transfer from the air impingementto the food product may be optimized. As to be described below, this canalso be done in conjunction with microwave modulations.

In addition, the configuration of the nozzles 108, 109 and the airmodulating cover 125 for controlling the flow rate of each nozzle asillustrated in FIG. 1 and described above may be operated in conjunctionwith the return air exit holes 115, 116 to modulate the air flow belowthe bottom of the support 112 as follows. For example, the airmodulating cover 125 may operate in synchronization with the opening andclosing the gates for the left and the right return air exit holes 115and 116, respectively. When the air modulating cover 125 is positionedas illustrated in FIG. 4A so that the air impingement comes from onlythe right nozzles 109 toward the left half of the cooking chamber 101,there is consequently a concentration of air flows around the left sideof the support 112 compared to the minimal air flows around the rightside of the support. By keeping the gates of the left return air exitholes 115 closed and the gates of the right return air exit holes 116open, the concentration of air flows from around the left side of thesupport 112 is forced to flow below the full horizontal width of thesupport 112 from the left end to the right end and exit through theright return air exit holes 116. On the other hand, when the airmodulating cover 125 is positioned as illustrated in FIG. 4C so that theair impingement comes from only the left nozzles 108 toward the righthalf of the cooking chamber 101, there is consequently a concentrationof air flows around the right side of the support 112 compared to theminimal air flows around the left side of the support. By keeping thegates of the right return air exit holes 116 closed and the gates of theleft return air exit holes 115 open, the concentration of air flows fromaround the right side of the support 112 is forced to flow below thefull horizontal width of the support 112 from the right end to the leftend and exit through the left return air exit holes 115. In this way,the air modulating cover 125 and the controller for opening and closingthe gates of the return air exit holes 115, 116 can modulate thedirection of return air flow beneath the support 112, thereby maximizingthe use of the air returning to the return air plenums 119, 120,facilitating the heat transfer to bottom of the support 112 (andconsequently the bottom of the food product 114 placed on the support112) and thereby further optimizing the cooking efficiency of the oven100. In an alternative embodiment of the present invention, the oven 100may further comprise another set of nozzles for providing additional hotair flow or air impingements to the bottom of the support 112 to furtherimprove the cooking efficiency of the oven 100.

The nozzles 108, 109 are designed in view of optimizing the airimpingements into the cooking chamber 101 and, more importantly, theoverall cooking efficiency of the oven 100. Various factors may be takeninto account in the design of the nozzles 108, 109 in this regard. Asnoted in the Background section, the more distant the cross section ofan air plume or a hot air column is from the nozzle exit orifice 118,the greater its diameter/cross-sectional area becomes, resulting inreduction in the efficiency of the air impingement. Such expansion ofthe air plume may be reduced by increasing the speed of the hot airflowing from the nozzles (or the flow rate of the nozzles), which may beachieved by a suitable configuration of the shape and dimension of thenozzles 108, 109. For example, increasing the height of the nozzles mayfacilitate an increase in the velocity of the air flowing through thenozzles.

However, the flow rate of the nozzles may be limited by the capacity,size, and/or power requirement of the hot air blower 203. In addition,while the increase in the flow rate of the nozzles may improve theefficiency of the air impingement, it needs to be counterbalanced by theconcern for the spotting problem as discussed in the Background section,as well as the concern for the potential damages to the food product114, in particular its visual appearance, due to the rapidly moving hotair. Furthermore, the desire to increase the height of the nozzles 108,109 to increase their flow rate needs to be counterbalanced by the needto keep the height, and therefore the size, of the oven 100 to a minimumin order to optimize its overall cooking and operating efficiency. Whenthese factors are taken into consideration, it is found that the optimalefficiency in air impingement and optimal cooking efficiency may beachieved with the nozzles 108, 109 having a height of approximately 3inches and an air speed at the nozzle exit orifice of roughly 25 milesper hour when the food product 114 is between 4 and 12 inches from thenozzle exit orifices.

It is also found that the effective length of the air plume or airimpingement generally increases with the increase in the ratio of thearea of the nozzle inlet orifice 117 to the area of the nozzle exitorifice 118. Accordingly, the ratio needs to be taken into account whenoptimizing the efficiency of the air impingement and the overall cookingefficiency of the oven 100. For a nozzle having the height of 3 inches,it is found that the optimal ratio of the nozzle inlet orifice 117 areato the nozzle exit orifice 118 area is roughly 4:1. While a ratiogreater than this optimal ratio still leads to a greater effectivelength in the air plume, a diminished return appears to result from anyadditional increase in the ratio.

In at least one alternative embodiment of the present invention, insteadof a row of nozzles 109 as shown, for example, in FIG. 3, a tube asshown in FIGS. 6B may be used to provide a hot air flow or impingementinto a cooking chamber of the oven. FIGS. 6A and 6B illustraterespectively one possible example of a tube before and after assembly.FIG. 6A shows components 608 and 609 for a tube body and one or moreslats or spacers 610. These components may be made of sheet metal. FIG.6B shows the tube 600 after these components are assembled together.Each tube has a tube inlet 601 coupled to an air conduit and/or airinlet housing of the oven to receive a heated gas, and a tube outlet 602coupled to a cooking chamber of the oven to provide the heated air intothe cooking chamber in the form of a hot air plume array. The tube 600of FIG. 6B could be a cheaper alternative to a row of nozzles whileproviding a substantially similar performance.

In this exemplary embodiment, the tube 600 may be in the shape of aninverted truncated triangular prism, with the tube inlet 601corresponding to the base of the prism and the tube outlet 602corresponding to the truncated top of the prism. As shown in FIG. 6B,the tube inlet 601 is larger than the tube outlet 602 at a ratiooptimized to form a tight plume of heated gas. Preferably, the dimensionof the tube 600 is designed to optimize the formation of a plume arrayof heated gas and thereby the performance of the cooking oven. Thelength of the tube is preferably long enough to establish a directionalflow of heated gas in the form of a plume, but not too long so as torequire the height of the cooking oven to be objectionable in terms ofcost and size considerations. Each tube is preferably wide enough tointroduce a sufficient volume of heated gas into the cooking chamber torapidly cook a food product in the cooking oven. At the same time, thetube outlet 602 is preferably narrow to facilitate the formation of atight plume. The tube 600 illustrated in FIG. 6B is an exemplaryembodiment taking into account these foregoing considerations. Unlikethe columns of heated air having a row of circular cross sections, suchas the one generated by a row of nozzles 109 shown in FIG. 3, a plumearray generated by the tube 600 in FIG. 6B is a planar band of movingheated gas having a rectangular cross section, substantially narrow inone direction but substantially wide in the perpendicular direction.

As shown in FIGS. 6A and 6B, the slats or spacers 610 may be placedwithin the inside of the tube 600, uniformly spaced in parallel. Thespacers 610 serve to prevent microwave energies in a cooking chamberfrom entering the tube 600. For this purpose, the spacers 610 arepreferably less than 1.2 inches spaced apart from each other. FIGS. 6Aand 6B shows that each of the spacers 610 may extend from the tubeoutlet 602 to the tube inlet 601. In an alternative embodiment, eachspacer 610 may extend, for example, only about half an inch inward fromthe tube outlet 602. While both examples serve to substantially preventmicrowave entry into the tube 600, it appears that the longer version ofthe spacer 610, extending from the tube outlet 602 to the tube inlet 601as shown in FIGS. 6A and 6B, better enables the evenness of the hot airflow along the width of the tube compared to the shorter version.

Analogous to the air modulating cover 125 of FIG. 1, a flap 603 as shownin FIG. 6C may be used to control the air flow through the tube 600 bycovering and opening the tube inlets 601. The flap 603 may be moved toopen and close the tube 600 by a lever arm 605, which may be in turndriven by a solenoid 604. FIG. 6C shows the flap 603 in open positionand FIG. 6D shows the flap 603 in closed position. A bracket 606 may beprovided to hold the solenoid 604 and the lever arm 605. Preferably, thebracket 606 is designed to minimize heat transfer from the oven plenumto the solenoid 604. As shown in FIG. 6D, the flap 603 preferably hassubstantially louvered edges 610 or other means to minimize any airleakage through the flap when closed.

In an alternative embodiment not shown in any drawing, the opening andclosing of the flap may be driven by one or more motors. In anotheralternative embodiment, the oven with two tubes may have one motordriving the two flaps for the two tubes. The motor may be configured toopen the flap for one tube, while keeping the other tube closed,permitting the alternate opening and closing between the two tubes.

For a cooking oven having a bottom air plenum through which a portion ofheated air can be diverted to the bottom of the cooking chamber, theflap 603 may also serve as a damper valve or bottom air diverter. Bycontrolling the degree of opening of the flap 603 for letting the heatedair in through the tube 600, one may at the same time control the amountof heated air diverted to the bottom air plenum.

Referring back to FIG. 6C, the surrounding area 607 where the tube 600penetrates the top of a cooking chamber is preferably firmly sealed toprevent any air leakage into the cooking chamber.

The exemplary embodiment of the present invention incorporating the tube600 as means of hot air impingement may further comprise a return airopening for allowing the gas from the plume arrays generated by the tube600 to return from the cooking chamber to the air conduit. One exampleof such return air opening is the return air exit holes 115, 116 shownin FIG. 1. Another example is one or more rectangular openings.Preferably, the return air opening is positioned substantially at oralong the intersection of the direction of the plume array and the wallof the cooking chamber. In this configuration, the heated air from theplume array generated by the tube 600 would strike a food product at anangle and is drawn across the surface of the food product toward itsedges and the edge of the support and then finally toward the return airopening. It is found that this configuration further improves the heattransfer between the heated gas and the food product.

Referring back to FIGS. 1 and 2 and turning now to the microwave-cookingfeature of the present invention, in addition to the air circulation andimpingement means, the hybrid oven 100 further comprises a pair ofmicrowave resonators 104 and 105, which are respectively positioned atthe opposite upper corners of the cooking chamber 101 to launchmicrowave energies respectively generated by magnetrons 102 and 103 intothe cooking chamber 101. The microwave resonator 104, 105 may be in theform of a waveguide, such as a slotted waveguide. While the oven 100according to the exemplary embodiment in FIG. 1 uses two magnetrons 102and 103, the present invention is not necessarily limited by the numberof magnetrons to generate microwave energies to be guided and launchedby the microwave resonators 104 and 105 into the cooking chamber 101.Furthermore, depending on the physical configuration of the support andthe cooking chamber of the oven, the positions of the microwaveresonators may be selected from various possible choices. For example,in an alternative embodiment, a pair of microwave resonators may bepositioned respectively at the opposite bottom corners of the cookingchamber. In yet another alternative embodiment, a pair of microwaveresonators may be positioned respectively at the upper and the lowerportions of a side wall of the cooking chamber to apply the microwaveenergy sideways to a food product held by a vertically positionedsupport such as a skewer.

Each microwave resonator 104, 105 may comprise a upper resonator 130,132 coupled to the corresponding magnetron 102, 103 to receivemicrowaves therefrom and a lower resonator 131, 133 coupled to thecooking chamber 101. The upper resonator 130, 132 functions to matchwith the corresponding magnetron 102, 103 and to guide the microwaveenergy therefrom to the lower resonator 131, 133. The lower resonator131, 133 functions to match the upper resonator 130, 132 to the cookingchamber 101 and to launch the microwave energy from the upper resonator130, 132 into the cooking chamber 101. The opening of the lowerresonator 131, 133 into the cooking chamber 101 may be covered by a lidmade of quartz so that the microwave radiation being transmitted throughthe lid from the lower resonator may become polarized. It is found thatthe optimal microwave efficiency may be achieved when the verticalheight of the lower resonator 131, 133 equals one quarter of themicrowave wavelength in free space (approximately 1.2 inches) and atleast one horizontal width of the lower resonator 131, 133 equals thewavelength of a standing microwave within the upper resonator 130, 132(e.g., about 6.2 inches based on a suitable dimension of the upperresonator).

Another exemplary configuration of a microwave resonator is shown inFIGS. 7A, 7B and 7C. FIG. 7A is an elevational side view of a microwaveresonator 700; FIG. 7B is a bottom plan view of the microwave resonator700; and FIG. 7C is a side perspective view of a component of themicrowave resonator 700. The configuration of the microwave resonator700 is designed to optimize the efficiency of microwave-to-heat energyconversion. The microwave resonator 700 comprises an upper resonator 701coupled to a magnetron and a lower resonator in the form of twofeedhorns 702 and 703 with openings to a cooking chamber of the oven.

As shown in FIG. 7C, each feedhorn 702 is in the shape of a truncatedrectangular pyramid, with the truncated top forming a top rectangularaperture 704 and the base of the pyramid forming a bottom rectangularaperture 705 of the feedhorn 702. The top aperture 704 is open to thecavity of the upper resonator 701 and the bottom aperture 705 is open tothe cooking chamber. The size of the top aperture is smaller than thesize of the bottom aperture, and their dimensions and ratio as well asthe height of the feedhorn 702, 703 may be adjusted to optimize themicrowave efficiency. FIG. 7B shows that the two feedhorns 702 and 703coupled to the upper resonator 701 are arranged substantially inparallel, but diagonally off-set with respect to each other. There maybe other alternative arrangements of the two feedhoms 702 and 703 thatcan further optimize the microwave efficiency.

Referring back to FIGS. 1 and 2, the pair of microwave resonators 104and 105, in particular their respective lower resonators 131 and 133,are adapted to direct the microwave radiation and energies in respectivegeneral directions 121 and 122 as indicated by the dotted lines comingout of the lower resonators 131 and 133. These directions 121 and 122are at an angle with respect to the vertical axis of the cooking chamber101 (or the horizontal plane of the support 112) and cross at a point129 at a distance from the support 112, preferably vertically above themidpoint between the left and the right sides of the support 112. Theoven 1 00 may be configured in such a way that this microwave crossingpoint 129 may take place above the upper surface of any food product 114placed on the support 112. In the alternative embodiment wherein themicrowave resonators are respectively positioned at the opposite bottomcorners of the cooking chamber, the microwave crossing point may belocated at a distance below the support. In the yet another alternativeembodiment wherein the microwave resonators are positioned on a sidewall of the cooking chamber, the microwave crossing point may be locatedat a horizontal distance from the vertical midpoint of the verticallypositioned support.

As indicated by the direction 121, the microwave resonator 104 at theleft upper corner of the cooking chamber 101 may be adapted to directthe microwave radiation toward the right half of the cooking chamber101, preferably toward a general area in the proximity of the right sideof the support 112. In mirror symmetry as viewed in FIG. 1, themicrowave resonator 105 at the right upper corner of the cooking chamber101 is adapted to direct the microwave radiation toward the left half ofthe cooking chamber 101 as indicated by the general direction 122,preferably toward a general area in the proximity of the left side ofthe support 112. Accordingly, the left and the right microwaveresonators 104 and 105 are configured to generally direct the respectivemicrowave energies to the opposite portions of the food product 114placed on the support 112. It should be appreciated that the “left side”and the “right side” of the support 112 to which the respectivemicrowave energies from the microwave resonators 104 and 105 aregenerally directed may correspond to any opposite portions of a foodproduct placed on or held by the support. There may be various possiblechoices for the “left side” and the “right side” of the supportdepending on the physical configuration of the support and the cookingchamber.

The angle formed by the directions 121 and 122 with respect to thevertical axis of the cooking chamber 101 is determined by where therespective microwave radiation from the microwave resonators 104 and 105are targeting. As an example, FIG. 1 shows that the microwave directions121 and 122 form an angle of roughly 45 degrees with respect to thevertical axis of the cooking chamber 101 and meet at the crossing point129 at an angle of roughly 90 degrees. However, these angles may varydepending on the dimensions of the cooking chamber 101 and the support112, as well as the relative positions of the microwave resonators 104and 105.

The oven 100 may further comprise a microwave modulator (not shown inthe figures) for controlling the amount of the microwave radiation andtheir energies coming out of each of the microwave resonators 104 and105 into the cooking chamber 101. The microwave modulation may beachieved by various means. One example of microwave modulation can beachieved by simply switching on and off the power to each of themagnetrons 102 and 103, either manually or by some suitable automaticcontrol means. In another example, the microwave modulation may beachieved by a voltage regulator capable of varying the voltage appliedto each of the magnetron 102 and 103 in a controlled manner. Themicrowave modulator having an automatic control means may facilitate aperiodic change in the power or voltage applied to each of themagnetrons 102 and 103, thereby creating a periodic modulation (e.g.,sinusoidal modulation, periodic step function modulation, etc.) in timeof the microwave energy radiating out of each of the microwaveresonators 104 and 105. By periodically alternating between the left andthe right magnetrons 102 and 103, the microwave modulator may provideperiodic modulations in the microwave energies respectively from theleft and the right microwave resonators 104 and 105 that have the sameamplitude and period, but differ in phase by 180 degrees. In addition,by maintaining the total microwave energies generated by both the leftand the right magnetrons 102 and 103 to be constant (e.g., by turningoff one magnetron while the other magnetron is on, or by providingperiodic modulations in the voltages provided to the magnetrons 102 and103 that have the same amplitude and period, but differ in phase by 180degrees), the sum of the periodically modulated microwave energies fromboth the left and the right microwave resonators 104 and 105 likewiseremains constant.

The configuration of the microwave resonators 104 and 105, illustratedin FIGS. I and 2, in conjunction with the above-described microwavemodulator may be operated to cause a time-dependent spatial variation inthe net microwave energy applied to the food product 114 placed on thesupport 112 in the cooking chamber 101 in the following exemplary way.Referring back to FIG. 1, for a predetermined time period, the microwavemodulator turns on only the left magnetron 102 while keeping the rightmagnetron 103 turned off, thereby allowing microwave energy to radiateonly from the left microwave resonator 104. As indicated by the generaldirection 121 of the microwave radiation from the left microwaveresonator 104, this configuration causes the net microwave energy to beconcentrated in the area in the right half of the cooking chamber 101,preferably in the general area in the proximity of the right side of thesupport 112.

After this time period, the microwave modulator keeps both the left andthe right magnetrons 102 and 103 on for another predetermined timeperiod, thereby allowing both the left and the right microwaveresonators 104 and 105 to radiate microwave energies into the cookingchamber. It is found that in general, the microwaves radiating from boththe left and the right microwave resonators 102 and 103 do not interferewith each other so as to cancel the net microwave energy. Accordingly,it is observed that in this configuration, the net microwave energy islargely concentrated in the middle portion of the support 112,preferably in the general area around the midpoint between the left andthe right sides of the support 112 and preferably in the center of thefood product 114 placed on the support 112 in the cooking chamber 101.

Next, for yet another predetermined time period, the microwave modulatorkeeps the right magnetron 103 on while maintaining the left magnetron102 turned off of the power, thereby allowing only the right microwaveresonator 105 to radiate the microwave energy into the cooking chamber101. As indicated by the general direction 122 of the microwaveradiation from the right microwave resonator 105, this configurationcauses the net microwave energy to be concentrated in the area in theleft half of the cooking chamber 101, preferably in the general area inthe proximity of the left side of the support 112.

In this way, the concentration of the net microwave energy radiated fromthe left and the right microwave resonators 104 and 105 may “sweep”across the food product 114 in the cooking chamber 101 from the right tothe left and vice versa over time in a controlled manner, therebyfacilitating even horizontal distribution of heat energy transfer fromthe microwave radiation to the food product and further improving themicrowave efficiency and the overall cooking efficiency of the oven 100.Furthermore, compared to the conventional high-speed cooking ovens basedon microwave, this selective directionality of the net microwave energyhelps to reduce the microwave radiation loss to the walls or otherspaces of the cooking chamber 101, thereby optimizing the microwaveefficiency and the overall cooking efficiency of the oven 100.

The capability of providing a time-dependent spatial variation in thenet microwave energy may also be applied to overcome or alleviate theinefficiency arising from the water steam carrying away thermal energyfrom the food product starting at the temperature of 212° F. asdescribed in the Background section. For example, referring to FIG. 1,the microwave modulator first keeps the left magnetron 102 on whilemaintaining the right magnetron 103 turned off so that the net microwaveenergy is concentrated in the proximity of the right side of the foodproduct 114. This configuration is maintained until the right side ofthe food product 114 reaches a temperature slightly under 212° F. Next,the microwave modulator keeps both the left and the right magnetrons 102and 103 on, causing the net microwave energy to be generallyconcentrated in the middle of the food product 114. When the middleportion of the food product 114 reaches a temperature slightly under212° F., then the microwave modulator turns off the left magnetron 102,while keeping the right magnetron 103 on, causing the net microwaveenergy to be concentrated in the proximity of the left side of the foodproduct 114. This configuration is maintained until the temperature ofthe left side of the food product 114 reaches slightly under 212° F.Meanwhile, the heat energies previously transferred to the right sideand the middle portion of the food product 114 are dispersed throughoutthe inner mass of the food product 114. The above microwave modulatingsteps may be repeated, periodically in time, until the internaltemperature of the food product 114 in the cooking chamber 101 reaches adesired level.

By maintaining the temperature of the different portions of the surfaceof the food product 113 slightly under 212° F. and allowing them todisperse the transferred heat energies to the inner mass of the foodproduct alternately at different times, the loss of thermal energy tothe water steam from the surface of the food product may be minimizedand therefore the efficiency of heat transfer from the microwave energyto the food product may be optimized.

Under the present invention, the operation settings of the oven 100 maycomprise various possible combinations and sequences of open and closeconfigurations of the left and the right nozzles 108 and 109 and on andoff configurations of the left and the right magnetrons 102 and 103. Inaddition, the operations of the air modulator (e.g., in the form of themovable air modulating cover 125 in FIG. 1) for controlling the airimpingement and the microwave modulator for controlling the microwaveradiation may be coordinated and synchronized with each other to achievethe desired heat transfer effect. In one possible configuration, the airmodulator and the microwave modulator may operate in phase in thefollowing exemplary way. Referring to FIG. 1, for a predetermined timeperiod, the air modulating cover 125 is positioned to keep the rightnozzle 109 open and the left nozzle 108 closed (as illustrated in FIG.4A), while the microwave modulator keeps the right magnetron 103 on andthe left magnetron 102 off. For the next predetermined time period, theair modulating cover 125 is positioned to keep both the right and theleft nozzles 109 and 108 open (as illustrated in FIG. 4B), while themicrowave modulator keeps both the right and the left magnetrons 103 and102 on. For the third predetermined time period, the air modulatingcover 125 is positioned to keep the left nozzle 108 open and the rightnozzle 109 closed (as illustrated in FIG. 4C), while the microwavemodulator keeps the left magnetron 102 on and the right magnetron 103off. As a result, the effects of the net air impingement and microwaveenergies “sweeping” across the food product 114 from one side to theother in time are in phase and therefore amplified.

On the other hand, since the heating by the air impingement and themicrowave heating cause different kinds of impacts on the food product114, one might instead desire to have the air modulator and themicrowave modulator to operate out of phase so as to avoid thesimultaneous heating of the same portion or side of the food product 114in the cooking chamber 101 by both the air impingement and the microwaveenergy. To illustrate one exemplary out-of-phase operation by the airmodulator and the microwave modulator, an alternative embodiment capableof opening and closing both the left and the right nozzles 108 and 109at the same time is used. For the first predetermined time period, theair modulator keeps the right nozzle 109 open and the left nozzle 108closed, while the microwave modulator keeps the left magnetron 102 onand the right magnetron 103 off. For the next predetermined time period,the air modulator keeps both the right and the left nozzles 109 and 108closed, while the microwave modulator keeps both the right and the leftmagnetrons 103 and 102 on. For the third predetermined time period, theair modulator keeps the left nozzle 108 open and the right nozzle 109closed, while the microwave modulator keeps the right magnetron 103 onand the left magnetron 102 off. For the fourth predetermined timeperiod, the air modulator keeps the right nozzle 109 open and the leftnozzle 108 closed, while the microwave modulator keeps the leftmagnetron 102 on and the right magnetron 103 off, as in the firstpredetermined time period. For the fifth predetermined time period, theair modulator keeps both the right and the left nozzles 109 and 108open, while the microwave modulator keeps both the right and the leftmagnetrons 103 and 102 off. For the sixth and the final predeterminedtime period of one cycle, the air modulator keeps the left nozzle 108open and the right nozzle 109 closed, while the microwave modulatorkeeps the right magnetron 103 on and the left magnetron 102 off, as inthe third predetermined time period. As the result of this out-of-phaseoperations by the air modulator and the microwave modulator, there is nosimultaneous heating of the same portion or side of the food product 114by both the air impingement and the microwave energy.

Other features of the hybrid oven 100 are also designed in view ofoptimizing the microwave efficiency, i.e., to maximize the amount of themicrowave energy directed to the food product 114 and minimize theamount of the microwave energy lost to the cavities, plenums,magnetrons, etc. or radiated away from the food product 114. Forexample, the diameter of the nozzle exit orifice 118 is sized to preventmicrowave energies from entering the nozzle and thereby becomingdissipated away rather than being applied to the food product 114. It isfound that the diameter of approximately 0.75 inches for the nozzle exitorifice 118 may be able to keep microwave energies from entering thenozzles, thereby optimizing the microwave efficiency in the oven 100.

The support 112 may be adapted to rotate around the vertical axis 135 atits center. Such rotation of the support 112 help to alleviate theproblem of horizontal unevenness in the microwave heat energydistribution. In addition, the oven 100 may further comprise an elevatoror an elevating mechanism to control and modulate the height of thesupport 112 with respect to the top and bottom of the cooking chamber101. As an example, FIG. 1 shows the support 112 elevated to a higherposition 113 vertically along the axis 135. This may be achieved eithermanually or by a suitable electromechanical elevation control means.Such modulation of the height of the support 112 may be used toalleviate the problem of vertical unevenness in the microwave heatenergy distribution.

The optimal microwave efficiency may also be achieved by matching thesize of the cooking chamber 101 with the microwave load. It is foundthat the optimal matching can be achieved by sizing preferably all, butat least one, of the vertical height, and horizontal width and depth ofthe cooking chamber 101 (as viewed in FIG. 1) in integer multiples ofthe microwave wavelength (approximately 4.82 inches in free space). Suchdimensions of the cooking chamber 101 facilitate the accommodation ofstanding microwaves in the cooking chamber 101, thereby minimizing thereflection of microwaves at the walls of the cooking chamber and theresulting loss of the microwave energy to the cavities, plenums,magnetrons, etc. Hence, to optimize the microwave efficiency, preferablyall, but at least one, of the vertical height, and the horizontal widthand depth of the cooking chamber 101 of the oven 100 is sized in integermultiples of the microwave wavelength, or selected from one of 4.82inches, 9.64 inches, 14.46 inches, 19.28 inches, 24.10 inches, etc.

The present invention accommodates cooking ovens of various sizes andcapacities. FIGS. 8A, 8B, and 8C illustrate various partial views of anexemplary small version of a hybrid cooking oven based on a combinationof hot air impingement and microwave; FIGS. 9A, 9B, and 9C illustratevarious partial views of an exemplary medium version, which is in manyaspects similar to the one shown in FIGS. 1-3; and FIGS. 10A, 10B, and10C illustrate various partial views of an exemplary large version.These figures are merely schematic illustrations based on variouspartial views and are not intended to be complete or reflect the exactdimensions, scales or relative proportions of the oven or componentsthereof, or the full engineering specification thereof, which should beapparent to those skilled in the art. Furthermore, while these figuresshow various internal oven components exposed to the outside forillustrative purposes, the commercial versions of these ovens would mostlikely have a housing to encase these components for safety, aestheticand other reasons. In addition, although these exemplary embodiments ofthe present invention are shown to use two tubes of the type shown inFIGS. 6B, 6C, and 6D as means of hot air impingement and one or moremicrowave resonator of the type shown in FIGS. 7A, 7B, and 7C as meansof microwave energy propagator, it should be appreciated that othervarious alternative types and configurations may be used in theirplaces.

Referring now to FIGS. 8A, 8B, and 8C, therein illustrated is anexemplary small version of a hybrid cooking oven 800. FIG. 8A is afrontal perspective view of the hybrid oven 800 with its door 801 open;FIG. 8B is a partial frontal cross-sectional view of the oven 800 ofFIG. 8A, with the view of a magnetron 804 and microwave resonator 805taken out for illustrative purpose; and FIG. 8C is a perspective view ofthe oven 800 from the left rear. The oven 800 comprises a cookingchamber 802, which is adapted to receive a food product on a support 803for cooking. The exemplary external dimension of the hybrid cooking oven800 is 14 inches wide, 28 inches deep, and 22 inches tall, and theexemplary dimension of the cooking chamber 802 is 9.6 inches wide, 12inches deep, and 9.6 inches tall.

As means for providing hot air impingement from the top of the cookingchamber, the oven 800 has two tubes 806 and 807 for generating plumearrays of heated gas and introducing them into the cooking chamber 802.These tubes 806 and 807 may be positioned on the top of the cookingchamber as shown in FIG. 8B. Each of the tubes 806 and 807 comprises atube inlet coupled to an air inlet housing and a tube outlet coupled tothe cooking chamber 802. The tubes 806 and 807 may be of the type andconfiguration shown in FIGS. 6B, 6C, and 6D, and may further comprise aflap for each tube as shown in FIGS. 6B, 6C, and 6D for covering andopening the tube inlet to control the heated air flow through the tube806, 807. Solenoids 808 and 809 may be used to drive the flaps to openand close. As noted above, brackets 813 and 814 may be used to hold thesolenoids 808 and 809 respectively so that the heat transfer from theoven plenum to the solenoids can be minimized.

In this exemplary embodiment, the tube inlets for the two tubes 806 and807 are respectively encased in separate air inlet housings 810 and 811,which are connected through an air conduit 812. The tubes 806 and 807are configured to respectively direct their plume arrays towardsubstantially opposite portions of the support 803 at a non-zero angleless than 90 degrees with respect to the surface of the support. In thisconfiguration, the directions of the plume arrays from the tubes 806 and807 cross each other above the food product placed on the support 803.

The oven 800 further comprises return air openings 815 and 816 on bothside walls of the cooking chamber 802. The return air opening 815 ispreferably positioned substantially at or along the intersection of thedirection of the plume array generated by the tube 807 and the side wallof the cooking chamber 802. Likewise, the return air opening 816 ispreferably positioned substantially at or along the intersection of thedirection of the plume array generated by the tube 806 and the side wallof the cooking chamber 802. The return air openings 815 and 816 allowthe gas from the plume arrays generated by the tubes 807 and 806 toreturn from the cooking chamber 802 to the air conduit 812 via returnair plenums 817 and 818 and one or more intermediate conduits,respectively.

The air conduit 812 allows gaseous communication from other parts of theoven to the two air inlet housings 810 and 811. While not shown in thefigures, a thermal energy source, such as parallel heating coils, may becoupled to or disposed in the air conduit 812 to heat the air disposedtherein. The oven 800 has a hot air blower 819 which serves to circulatethe air between the cooking chamber 802, the return air plenums 817 and818, the air conduit 812, and the air inlet housings 810 and 811. Thehot air blower 819 is driven by a blower motor 824, which may be asingle speed or variable speed.

The oven 800 also has bottom air inlets 820 which are positioned belowthe support 803 substantially at the bottom of the cooking chamber 802to direct a hot air flow to the underside of the support 803. This hotair to the bottom air inlets 820 is supplied by a bottom air inletplenum 821, which is connected to, and diverts the heated gas from, theair conduit 812. In this oven 800, the hot air blower 819 serves tocirculate the heated gas not only to the air inlet housings 810 and 811on the top of the cooking chamber 802, but also to the bottom air inletplenum 821 below the bottom of the cooking chamber.

The hybrid oven 800 also has one magnetron 804 for generating microwaveenergy. The magnetron 804 is coupled to a microwave resonator 805, whichis configured to propagate the microwave energy from the top of thecooking chamber straight down into the cooking chamber 802. Themicrowave resonator 805 may be of the type shown in FIGS. 7A, 7B, and7C, and may comprise an upper resonator (shown in FIGS. 8A and 8C) andtwo feedhoms (not shown in the figures) as a lower resonator, whosebottom ends respectively protrude into the cooking chamber 802 throughthe two rectangular apertures 822 and 823 on the top of the cookingchamber, as shown in FIG. 8B. Alternatively, the microwave resonator 805may be any other waveguide known in the art.

Referring now to FIGS. 9A, 9B, and 8C, therein illustrated is anexemplary medium version of a hybrid cooking oven 900. This exemplaryembodiment is similar to the hybrid oven 100 illustrated in FIGS. 1-3 inmany aspects. FIG. 9A is a frontal perspective view of the hybrid oven900; FIG. 9B is a partial frontal cross-sectional view of the oven 900of FIG. 9A, with the view of magnetrons 930, 931 and their associatedmicrowave resonators 932, 933, 934, 935 taken out for illustrativepurpose; and FIG. 9C is a perspective view of the oven 900 from theright rear. The oven 900 comprises a cooking chamber 902, which isadapted to receive a food product on a support 903 for cooking. Theexemplary external dimension of the hybrid cooking oven 900 is 28 incheswide, 27 inches deep, and 24 inches tall, and the exemplary dimension ofthe cooking chamber 902 is 14.4 inches wide, 14.4 inches deep, and 10.2inches tall.

As means for providing hot air impingement from the top of the cookingchamber, the oven 900 has two tubes 906 and 907 for generating plumearrays of heated gas and introducing them into the cooking chamber 902.These tubes 906 and 907 may be positioned on the top of the cookingchamber as shown in FIG. 9B. Each of the tubes 906 and 907 comprises atube inlet coupled to an air inlet housing 910 and a tube outlet coupledto the cooking chamber 902. The tubes 906 and 907 may be of the type andconfiguration shown in FIGS. 6B, 6C, and 6D, and may furtherrespectively comprise flaps 927 and 928 for covering and opening thetube inlet to control the heated air flow through the tubes 906 and 907.Solenoids 908 and 909 may be used to respectively drive the flaps 927and 928 to open and close. As noted above, brackets 913 and 914 may beused to hold the solenoids 908 and 909 respectively so that the heattransfer from the oven plenum to the solenoids can be minimized.

In this exemplary embodiment, the tube inlets for the two tubes 906 and907 are both encased in a single air inlet housing 910. The tubes 906and 907 are configured to respectively direct their plume arrays towardsubstantially opposite portions of the support 903 at a non-zero angleless than 90 degrees with respect to the surface of the support. In thisconfiguration, the directions of the plume arrays from the tubes 906 and907 cross each other above the food product placed on the support 903.

The oven 900 further comprises return air openings 915 and 916 on bothside walls of the cooking chamber 902. The return air opening 915 ispreferably positioned substantially at or along the intersection of thedirection of the plume array generated by the tube 907 and the side wallof the cooking chamber 902. Likewise, the return air opening 916 ispreferably positioned substantially at or along the intersection of thedirection of the plume array generated by the tube 906 and the side wallof the cooking chamber 902. The return air openings 915 and 916 allowthe gas from the plume arrays generated by the tubes 907 and 906 toreturn from the cooking chamber 902 to an air conduit 940 via return airplenums 917 and 918, respectively.

While not shown in the figures, a thermal energy source, such asparallel heating coils, may be coupled to or disposed in the air conduit940 to heat the air disposed therein. The oven 900 has a hot air blower919 which serves to circulate the air between the cooking chamber 902,the return air plenums 917 and 918, the air conduit 940, and the airinlet housing 910. The hot air blower 919 is driven by a blower motor924 (not shown in FIG. 9C), which may be a single speed or variablespeed.

The oven 900 also has bottom air inlets 920 which are positioned belowthe support 903 substantially at the bottom of the cooking chamber 902to direct a hot air flow to the underside of the support 903. The hotair to the bottom air inlets 920 is supplied by a bottom air inletplenum 921. In this oven 900, the hot air blower 919 serves to circulatethe heated gas not only to the air inlet housing 910 on the top of thecooking chamber 902, but also to the bottom air inlet plenum 921 belowthe bottom of the cooking chamber. A portion of the heated air from thehot air blower 919 is diverted to the bottom air inlet plenum 921 via abottom air conduit 912.

The hybrid oven 900 also has two magnetrons 930 and 931 for generatingmicrowave energies for microwave cooking. Each of the magnetrons 930 and931 is coupled to a microwave resonator for propagating the microwaveenergy into the cooking chamber 902. The microwave resonator may be ofthe type shown in FIGS. 7A, 7B, and 7C, and may comprise an upperresonator 932, 934 coupled to the magnetron 930, 931, and a lowerresonator in the form of two feedhorns 933, 935, with an opening to thecooking chamber 902. Alternatively, the microwave resonators may be anyother waveguides known in the art.

FIG. 9A shows bottom apertures 936 of the feedhorns 933 for directingthe microwave energy propagation generated by the magnetron 930 andguided by the upper resonator 932 from the upper left corner of the topof the cooking chamber 902 substantially toward the right portion of thesupport 903. In this exemplary embodiment as shown in FIG. 9A, themicrowave resonators 932, 933 on the upper left corner of the top of thecooking chamber 902 and the microwave resonators 934, 935 on the upperright corner of the top of the cooking chamber 902 are configured torespectively direct the microwave energies to propagate generallytowards substantially opposite portions of the support 903 at a non-zeroangle less than 90 degrees with respect to the surface of the support.In this configuration, the propagation directions of the microwaveenergies from the microwave resonators from the both sides cross eachother at a distance from the support in the cooking chamber 902.

Referring now to FIGS. 10A, 10B, and 10C, therein illustrated is anexemplary large version of a hybrid cooking oven 1000. FIG. 10A is afrontal perspective view of the hybrid oven 1000 with its door 1001open; FIG. 10B is a partial frontal cross-sectional view of the oven1000 of FIG. 10A, with the view of magnetrons 1030, 1031 and theirassociated microwave resonators 1032, 1033, 1034, 1035 taken out forillustrative purpose; and FIG. 10C is a perspective view of the oven1000 from the right rear. The oven 1000 comprises a cooking chamber1002, which is adapted to receive a food product on a support 1003 forcooking. This exemplary large version may accommodate the support 1003in the form of an elevator or an additional elevating mechanism for thesupport 1003 so that the height of the support 1003 may be dynamicallyadjusted during the operation of the oven 1000. The exemplary externaldimension of the hybrid cooking oven 1000 is 30 inches wide, 26 inchesdeep, and 23 inches tall, and the exemplary dimension of the cookingchamber 1002 is 16.8 inches wide, 16.8 inches deep, and 12.6 inchestall.

As means for providing hot air impingement from the top of the cookingchamber, the oven 1000 has two tubes 1006 and 1007 for generating plumearrays of heated gas and introducing them into the cooking chamber 1002.These tubes 1006 and 1007 may be positioned on the top of the cookingchamber as shown in FIG. 10B. Each of the tubes 1006 and 1007 comprisesa tube inlet coupled to an air inlet housing 1010 and a tube outletcoupled to the cooking chamber 1002. The tubes 1006 and 1007 may be ofthe type and configuration shown in FIGS. 6B, 6C, and 6D, and mayfurther respectively comprise flaps 1027 and 1028 for respectivelycovering and opening the tube inlets of the tubes 1006 and 1007 tocontrol the heated air flow through the tubes. Solenoids 1008 and 1009may be used to respectively drive the flaps 1027 and 1028 to open andclose the air inlets to the tubes 1006 and 1007. As noted above,brackets 1013 and 1014 may be used to respectively hold the solenoids1008 and 1009 so that the heat transfer from the oven plenum to thesolenoids can be minimized.

In this exemplary embodiment, the tube inlets for the two tubes 1006 and1007 are both encased in a single air inlet housing 1010. The tubes 1006and 1007 are configured to respectively direct their plume arrays towardsubstantially opposite portions of the support 1003 at a non-zero angleless than 90 degrees with respect to the surface of the support. In thisconfiguration, the directions of the plume arrays from the tubes 1006and 1007 cross each other above the food product placed on the support1003.

The oven 1000 further comprises return air openings 1015 and 1016 onboth side walls of the cooking chamber 1002. The return air opening 1015is preferably positioned substantially at or along the intersection ofthe direction of the plume array generated by the tube 1007 and the sidewall of the cooking chamber 1002. Likewise, the return air opening 1016is preferably positioned substantially at or along the intersection ofthe direction of the plume array generated by the tube 1006 and the sidewall of the cooking chamber 1002. The return air openings 1015 and 1016allow the gas from the plume arrays generated by the tubes 1007 and 1006to return from the cooking chamber 1002 to an air conduit 1055 viareturn air plenums 1017 and 1018, respectively.

While not shown in the figures, a thermal energy source, such asparallel heating coils, may be coupled to or disposed in the air conduit1055 to heat the air disposed therein.

The oven 1000 also has bottom air inlets 1020 which are positioned belowthe support 1003 substantially at the bottom of the cooking chamber 1002to direct a hot air flow to the underside of the support 1003. The hotair flowing through the bottom air inlets 1020 is supplied by a bottomair inlet plenum 1021. As shown in FIG. 10C, the oven 1000 has twoindependently controllable hot air blowers 1019 and 1050. The top blower1019, driven by a top blower motor 1024, serves to direct the heated gasin the air conduit 1055 to the air inlet housing 1010 through a topblower outlet 1052. Meanwhile, the bottom blower 1050, driven by abottom blower motor 1051, serves to divert a portion of the heated gasdisposed in the air conduit 1055 to the bottom air inlet plenum 1021through a bottom blower outlet 1053. Each of the blower motors 1024,1051 may be a single speed or variable speed.

The hybrid oven 1000 also has two magnetrons 1030 and 1031 forgenerating microwave energies for microwave cooking. Each of themagnetrons 1030 and 1031 is coupled to a microwave resonator forpropagating the microwave energy into the cooking chamber 1002. Themicrowave resonator may be of the type shown in FIGS. 7A, 7B, and 7C,and may comprise an upper resonator 1032, 1034 coupled to the magnetron1030, 1031, and a lower resonator in the form of two feedhoms 1033,1035, with an opening to the cooking chamber 1002. Alternatively, themicrowave resonator may be any other waveguide known in the art.

In this exemplary embodiment, the microwave resonator comprising theupper resonator 1032 and the lower resonator 1033 on the upper leftcorner of the top of the cooking chamber 1002 and the microwaveresonator comprising the upper resonator 934 and the lower resonator 935on the upper right corner of the top of the cooking chamber 1002 areconfigured to respectively direct the microwave energies to propagategenerally towards substantially opposite portions of the support 1003 ata non-zero angle less than 90 degrees with respect to the surface of thesupport. In this configuration, the propagation directions of themicrowave energies from the microwave resonators from the both sidescross each other at a distance from the support in the cooking chamber1002.

One common feature shared by the various exemplary embodiments of thepresent invention illustrated in FIGS. 8-10 and described above is thetwo-tube arrangement for hot air impingement positioned at the top of acooking chamber. The two tubes are configured to respectively directplume arrays or planar plumes of heated air towards substantiallyopposite portions of the support for a food product, with the directionsof the plume arrays from the two tubes crossing above the food product.This feature is further illustrated in FIGS. 11A-11C.

In FIG. 11A, the left tube 1101 on the top of the cooking chambergenerates a plume array 1104 of heated air and directs it toward theright portion of a support 1103 of a cooking oven 1100. Although theplume array 1104 spreads out as it travels through the cooking chamber,the tube 1101 is configured and designed in such a way that the impactof the plume array 1104 is focused substantially on the right portion ofthe support 1103. Likewise, in FIG. 11B, the right tube 1102 on the topof the cooking chamber generates a plume array 1105 of heated air anddirects it toward the left portion of the support 1103. The tube 1102 isalso configured and designed in such a way that the impact of the plumearray 1105 is focused substantially on the left portion of the support1103. When both of the tubes 110 1 and 1102 are open and direct theirrespective plume arrays into the cooking chamber, their respective plumearrays collide above the support 1103, and the net result is that theimpact of the sum of these plume arrays 1106 is focused substantially onthe center of the support 1103, as shown in FIG. 11C.

The above-described capability of the tubes 1101 and 1102 to focus theimpact of one or more plume arrays substantially on a selected portionof the support 1103 not only provides the new degree of flexibility, butalso optimizes the utilization of the given amount of heated air incooking a food product. For example, if the surface area of a foodproduct placed on the center of the support 1103 is substantiallysmaller than the surface area of the support (e.g., a 6-inch sub placedon a 14.4 inch by 14.4 inch support), then one can maximize the contactbetween the heated air and the food product on the support by focusingthe heated air in the form of plume arrays substantially on the centerof the support, as shown in FIG. 11C. In this way, one can optimize theutilization of the heated air in cooking the food product, whileminimizing the application of the heated air to the area of the supportwhere the heated air is not needed (i.e., where the food product is notpresent).

In comparison, a typical conventional high-speed cooking oven usescolumns of heated air, which are designed to strike a food product at anangle substantially perpendicular to the surface of the food product. Byits design, the conventional high-speed oven applies the columns ofheated air over the entire surface of the support, without thecapability of focusing the heated air on a selected portion of thesupport. Hence, compared to the present invention, the conventionalhigh-speed oven is not only much less flexible, but also much lessefficient in utilizing the given amount of heated air in cooking a foodproduct, as much of the impinging air does not contact the food product.

Even for a food product with a relatively large surface area, thetwo-tube arrangement shown in FIGS. 11A, 11B and 11C is much moreefficient in utilizing the heated air than the conventional high-speedoven. Because the direction of the plume array of heated air from thetube 1101, 1102 is at a non-zero angle less than 90 degrees with respectto the surface of the support 1103, the heated air is drawn laterallyacross the surface of the food product after the impact and moves towardthe side edges of the support 1103. This lateral drawing of the heatedair across the food surface facilitates the heat transfer from theheated air to the food product. As discussed above, by positioning areturn air opening at or along the intersection of the direction of theplume array from the tube 1101, 1102 and the side wall of the cookingchamber, one may further enhance the effect of drawing the heated airlaterally across the food surface, thereby optimizing the cookingefficiency.

The above-described features and improvements in accordance with thepresent invention enable a high-speed cooking oven based on acombination of hot air impingement and microwave to deliver optimalcooking efficiency. Tangible benefits of this improvement in the cookingefficiency in the high-speed cooking technology are the reduction in thecooking time at a given electrical power supply, and alternatively, thereduction in the electrical power required to operate a high-speedcooking oven for a given cooking capacity (i.e., given cooking time). Asnoted in the Background section, because of their sub-optimal cookingefficiency, the conventional high-speed cooking ovens must operate on anelectrical power supply based on 220 volts or greater. By furtherimproving and optimizing the cooking efficiency under the presentinvention, the high-speed cooking technology based on a combination ofair impingement and microwave may now be extended with more productiveresults to ovens operating on an electrical power supply based on avoltage less than 220 volts, preferably a power supply based on avoltage between 110 and 125 volts and a current of 30 amperes or less,which is more widely available than the 220 volt-based power supply.Hence, the present invention enables the high-speed cooking technologyto find a wider range of applicability and customer base compared to theconventional high-speed cooking technology with the sub-optimal cookingefficiency.

While this invention has been described in conjunction with exemplaryembodiments outlined above and illustrated in the drawings, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, the exemplaryembodiments of the invention, as set forth above, are intended to beillustrative, not limiting, and the spirit and scope of the presentinvention is to be construed broadly and limited only by the appendedclaims, and not by the foregoing specification.

1. An oven for cooking a food product, comprising: a cooking chambercomprising a top, a bottom, and a support for receiving the food productfor cooking; one or more magnetrons; one or more microwave resonatorsfor directing a microwave energy generated by the one or more magnetronsinto the cooking chamber; a conduit and one or more air blowers forproviding a gas into the cooking chamber; a thermal energy source forheating the gas disposed in the conduit; a first tube for generating afirst plume array of the heated gas from the conduit and introducing itinto the cooking chamber; and a second tube for generating a secondplume array of the heated gas from the conduit and introducing it intothe cooking chamber, wherein the first and the second tubes areconfigured to respectively direct the first and the second plume arraystowards substantially opposite portions of the support at a non-zeroangle less than 90 degrees with respect to the surface of the support,with the directions of the first and the second plume arrays crossingeach other above the food product on the support in the cooking chamber.2. The oven of claim 1, further comprising an elevator for adjusting theheight of the support.
 3. The oven of claim 1, wherein the height of thesupport is dynamically adjustable to optimize the cooking efficiency andpower consumption for cooking the food product.
 4. The oven of claim 1,further comprising a return air opening for allowing the gas from thefirst and the second plume arrays to return from the cooking chamber tothe conduit.
 5. The oven of claim 4, wherein the return air openingcomprises: a first return air opening positioned substantially at oralong the intersection of the direction of the first plume array and thecooking chamber wall; and a second return air opening positionedsubstantially at or along the intersection of the direction of thesecond plume array and the cooking chamber wall.
 6. The oven of claim 1,wherein the conduit comprises one or more bottom air inlets, positionedsubstantially at the bottom of the cooking chamber, for diverting aportion of the heated gas to the bottom of the cooking chamber anddirecting it to the underside of the support.
 7. The oven of claim 6,further comprising an air modulator for controlling a flow rate of theheated gas through the one or more bottom air inlets.
 8. The oven ofclaim 1, wherein the one or more microwave resonators comprise one ormore waveguides.
 9. The oven of claim 1, wherein each of the one or moremicrowave resonators comprises an upper resonator coupled to the one ormore magnetrons and a lower resonator with an opening to the cookingchamber.
 10. The oven of claim 9, wherein the lower resonator comprisestwo feedhorns, each having a top aperture to the upper resonator and abottom aperture to the cooking chamber.
 11. The oven of claim 10,wherein the two feedhorns are placed substantially in parallel, butdiagonally off-set with respect to each other.
 12. The oven of claim 10,wherein each of the two feedhoms is in the shape of a truncatedrectangular pyramid with the bottom rectangular aperture correspondingto the base of the pyramid, and the top rectangular aperture is smallerthan the bottom rectangular aperture.
 13. The oven of claim 1, whereinthe dimensions of the microwave resonator are designed to optimize themicrowave-to-heat energy conversion.
 14. The oven of claim 1, whereineach of the first and the second tubes comprises a tube inlet coupled tothe conduit and a tube outlet to the cooking chamber.
 15. The oven ofclaim 14, wherein each of the first and the second tubes is in the shapeof an inverted truncated triangular prism with the tube inletcorresponding to the base of the prism.
 16. The oven of claim 14,wherein the area of the tube inlet is larger than the area of the tubeoutlet at a ratio substantially sufficient for forming a tight plume ofthe heated gas.
 17. The oven of claim 14, wherein the dimensions of thefirst and the second tubes are designed to optimize the formation of aplume of the heated gas having a long and narrow rectangular crosssection.
 18. The oven of claim 1, further comprising a first flap and asecond flap for respectively covering the first and the second tubes.19. The oven of claim 18, further comprising one or more motors fordriving the first and the second flaps to open and close.
 20. The ovenof claim 19, wherein the one or more motors are configured to open onlyone of the first and the second flaps, while keeping the other closed.21. The oven of claim 18, further comprising one or more lever armsdriven by one or more solenoids to open and close the first and thesecond flaps.
 22. The oven of claim 14, further comprising a first flapand a second flap for respectively covering the tube inlets of the firstand the second tubes.
 23. The oven of claim 22, wherein each of thefirst and the second flaps has substantially louvered edges to minimizeair leakage when closed.
 24. The oven of claim 14, wherein each of thefirst and the second tubes comprises one or more spacers to keep themicrowave energy from entering the tube.
 25. The oven of claim 6,wherein the one or more air blowers comprise: a first air blower fordirecting the heated gas in the conduit to the first and the secondtubes; and a second air blower for directing the heated gas in theconduit to the one or more bottom air inlets, wherein the first and thesecond air blowers are independently controllable.
 26. The oven of claim1, wherein the one or more air blowers comprise a single speed airblower.
 27. The oven of claim 1, wherein the one or more microwaveresonators comprise: a first microwave resonator for directing a firstmicrowave energy generated by the one or more magnetrons into thecooking chamber; and a second microwave resonator for directing a secondmicrowave energy generated by the one or more magnetrons into thecooking chamber, wherein the first and the second microwave resonatorsare configured to respectively direct the first and the second microwaveenergies to propagate generally towards substantially opposite portionsof the support at a non-zero angle less than 90 degrees with respect tothe surface of the support, with the propagation directions of the firstand the second microwave energies crossing each other at a distance fromthe support in the cooking chamber.
 28. The oven of claim 27, whereinthe one or more magnetrons comprise: a first magnetron for generatingthe first microwave energy; and a second magnetron for generating thesecond microwave energy.
 29. The oven of claim 27, wherein thepropagation directions of the first and the second microwave energiesare at a substantially 45-degree angle with respect to the surface ofthe support.
 30. The oven of claim 1, wherein the cooking chamber isdimensioned to match a microwave load of the oven.
 31. The oven of claim1, wherein the cooking chamber is dimensioned in integer multiples ofthe wavelength of the microwave energy.
 32. The oven of claim 31,wherein at least one of the length, width and height of the cookingchamber is sized in integer multiples of the wavelength of the microwaveenergy.
 33. The oven of claim 27, wherein the first microwave resonatoris positioned substantially near a first side of the top of the cookingchamber and the second microwave resonator is positioned substantiallynear a second side of the top of the cooking chamber, the first and thesecond sides being opposite sides of the top.
 34. The oven of claim 33,wherein the first side of the top comprises a left edge of the top andthe second side of the top comprises a right edge of the top.
 35. Theoven of claim 27, further comprising a microwave modulator forcontrolling each of the first and the second microwave energies.
 36. Theoven of claim 35, wherein the microwave modulator is adapted to cause atime-dependent spatial variation in the sum of the first and the secondmicrowave energies applied to the food product in the cooking chamber.37. The oven of claim 35, wherein the microwave modulator comprises avoltage regulator for modulating a voltage for the one or moremagnetrons.
 38. The oven of claim 35, wherein the microwave modulatorcomprises a switch for turning on and off an electrical power to the oneor more magnetrons.
 39. The oven of claim 1, further comprising an airmodulator for controlling respective flow rates of the heated gasthrough the first and the second tubes.
 40. The oven of claim 39,wherein the air modulator is adapted to cause a time-dependent spatialvariation in the sum of the first and the second plume arrays applied tothe food product in the cooking chamber.
 41. The oven of claim 1,wherein the directions of the first and the second plume arrays are at asubstantially 45-degree angle with respect to the surface of thesupport.
 42. The oven of claim 1, wherein the first tube is positionedsubstantially through a first half of the top of the cooking chamber,and the second tube is positioned substantially through a second half ofthe top.
 43. The oven of claim 14, wherein the conduit comprises acommon top air inlet plenum enclosing the tube inlets for both the firstand the second tubes.
 44. The oven of claim 14, wherein the conduitcomprises two separate top air inlet plenums respectively enclosing thetube inlets for the first tube and the tube inlets for the second tube.45. The oven of claim 7, wherein the air modulator comprises a dampervalve for the one or more bottom air inlets.
 46. The oven of claim 7,wherein the air modulator comprises a deflector in the conduit.
 47. Theoven of claim 7, wherein the air modulator comprises a bottom airdiverter in the conduit.
 48. The oven of claim 1, wherein: the firsttube is adapted to focus the first plume array substantially at one sideof the support, when the second tube is closed; the second tube isadapted to focus the second plume array substantially at the oppositeside of the support, when the first tube is closed; and the first andthe second tubes are adapted to focus the sum of the first and thesecond plume arrays substantially at the center of the support, whenboth are open.
 49. The oven of claim 48, further comprising: a firstreturn air opening positioned substantially at or along the intersectionof the direction of the first plume array and the cooking chamber wall;and a second return air opening positioned substantially at or along theintersection of the direction of the second plume array and the cookingchamber wall.
 50. The oven of claim 1, wherein the first and the secondtubes are configured to optimize the utilization of the first and thesecond plume arrays for cooking the food product whose surface area issubstantially smaller than the surface area of the support.
 51. The ovenof claim 1, wherein the oven is adapted to be powered by a voltage lessthan 220 volts.